.Net Foundation Design Reviews, 25 Jun 2019

Previous Meeting Next Meeting

⏯

youtube image

►

From YouTube: .NET Design Review: Nullability Custom Attributes

Description

We'll take a look at applications of new custom attributes to help the nullability analysis.

A

A

A

It's efficient and they fall into a few categories. There are attributes that allow you to say, even though something is attributed to not take know it might still take know, so that's allowed no the allowed null attribute.

A

Similarly, you can say this is attributed to take know, but we don't allow null and that's the disallowed null attribute and then the same kind of corollaries exists for the out direction, so you can say, even though something is that is attributed such that it doesn't look like or it may not. I may not return null. It actually can that's the maybe null and then there's even though it's something attributed to say that it could be null.

A

It actually can't be, and that's the not null attribute so basically that it's it's it's tweaking the direction so, for example, just in this very first case. Fine last, you know this.

A

Can this is the T here isn't constrained, so a developer could construct this with, say a string rather than a string question mark, but the semantics of mind, which then suggests that, because it returns a t, it's always going to return non null, but the semantics of fine last are to return null if the thing can't be found, and so even though someone may have called this with string rather than string question mark, we attribute the result is may be null because we may actually return them.

A

So that's one, that's one category. Then there are conditional variants on those where you can say in particular.

A

Well, you could basically say, and a parameter may be no when referring to the return return position, so you can say like upon the completion of this method. This parameter may may be known. That applies both to refs. It also can apply to an input position, so you can say like, for example, string is null or empty, we'll have a what is? It may be? No, when true on the string parameter, because if is null or empty returns returns true, then, obviously the input parameter.

A

Could have been known and then there's also a not null when and so on. Then there are also attributes that are around control flow. There's. It does not return, which is only about null ability. It's not about general control flow, just in knowable flow and also it does not return. When for a boolean parameter, we applied that to debug assert, for example, so debug assert has.

A

It does not return when false on its first argument and then there's also there's one more which is not null when not null which links together multiple parameters or return values. You can say this will not be no when another one is not long. I think that's all.

B

Yeah, it reads better and source because you get the name right. That's.

A

Sort of the scope of all this yeah all.

C

Right, so the system on camp is supposed to be complete right. These are the entire attributes that we think are correct. Is that right or there's some area, this additional system on time? No.

D

All the assemblies that I given they should have all the attributes that we thought we needed. Okay, so I.

C

Think that's missing, then, is not there. So these seem sensible to me given what you just explained. Suppose nobody in the warm objects to.

E

That and I recall correctly, maybe normal is usually put on a team, because if a value type that would actually change the return, there's like a question mark doesn't make sense, because the value type turns into it right.

A

Right it is, it can be used on non generics as well and that it's that's rarer, but it happens.

A

So, for example, we have, if you have a property where the getter might return null, but the center doesn't allow null. Then we have to specify the property as a t.

A

Sorry, the other direction right with a getter with the getter might return null in the setter. Does an exceptional one way of exposing that is to have the type B non null type, even if it's a concrete type rather than generic and to put may be null on it.

C

Makes sense all right.

A

You so resize guarantees that the array coming out will never be no, even though the array coming in could be, and so it's the says it will, it will not be no, even though you may have called this with a t question mark, or rather with that with a T or a question mark.

C

That's funny, though, because this you could express here right, I mean the weather. The array itself is not able or not that's expression. The.

A

Prop the problem, is you want the calls, after resize to not have to bang on the access to the array? So you know if let's say you have you've initialized a tee, open, brace, open bracket, close bracket question mark array equals no, and then you call resize ref array. You don't want to have to then use an exclamation point to access array after this call, if.

F

It shouldn't did them, be a question mark here. The array, the array itself is not nullable in this. No.

C

Like I mean, basically, if it's like this, you wouldn't be able to call it over T or a question mark right unless the knowledge.

C

E

Not Italo I'm. Sorry, sorry.

C

I think my problem here is that yeah this one will not show any question mark, but that probably is a question mark in sort will.

B

Be my hair, there is oh okay.

C

Dave accent, we basically say you can't pass me another Ray, but it will never give you back one exactly.

E

C

E

They make sense all right, let's cool off a little bit to index out that takes array. But if she already has yes so system array object, value value should be object, but even more, we just said we can't see clip. You can't see that okay, okay, so.

C

Just so this one, no it's like doing it again: they're generated the Jen API that I'm using there's not.

E

Thankfully, we've done we got question mark about the attributes are looking at Rebecca, okay, so the comment was for all ad eyes on okay, it's correct you.

B

C

Now here's where it gets pixie so.

A

Oh this one combined, it can return null. If you pass in to null delegates, then you're gonna get back out No.

A

So this is saying: if either A or B is not null, then your result is going to be non null as well.

C

That's the combination of these guys is or write each.

A

Each one has taken sort of interning. The result will be not null if a is not null. The result will be not null if B is not known.

C

That makes sense.

C

And this is busy or mine's generic question mark.

A

E

Noah's returned and allowed all was in yeah, correct.

C

If it needed two different attributes, because there are some cases where.

F

C

To plug there, yeah.

F

Crafts and crafts, where you can put include an opener different things, yeah.

C

Well also get a cookie cuz, I'm, sorry.

F

Steveo room.

C

Well, Steve, like judging by the sound earlier, he already had some breakfast.

A

It was my lunch but yeah we.

E

Could crumble a cookie over the I.

A

Appreciate that please do I'm.

D

G

One well I'll Santi: you can change.

F

The capacity number yet some not quite an easiest option to dimension. Oh I, think.

E

You can have some so much better.

D

That's true, yes,.

C

Well, those make sense yeah.

C

So that's an interesting one right, so we basically say it's not. Why empty? That's, basically the compiler that if you gave me something that is not now I love, boats.

B

A

This allows you to avoid using an exclamation point on value. If the compiler sees you're in a condition where you say, if not is null or empty and then you, you don't have to use an exclamation point.

B

B

A

It's true, the compiler knows nothing else. You know it was none right and that's best because it could have been non-null. If it returned true, it could have been non-null but empty. Your whitespace.

C

During an absolute well, that's just the way: okay, it's the fact that I didn't be open desert. That is be wondering if my they haven't.

F

Suddenly developed colorblindness, that's.

A

So these are interesting. The the common, the most common use of the win. These win attributes is on try methods where you have an out- and we say it's you know not know when true or maybe know and false and in general the rule is or the guideline is, if it's a non-generic you're, typically gonna, see and not know when true and if it's a generic you're, typically gonna, see them, maybe Nolan false.

A

Wait wait because if it's a non-generic, then we explicitly specify it. We know that that we know the null ability of the type that we're specifying, and so we can be strong about it. We can say we know that this will not be know when it's true. If it's a generic like let's say it's a dictionary of T key T value need to try get value, it's possible that you've constructed T value as a string question mark and then even if try get value returns. True, it may still be known.

A

So with most generics in most cases, we have no choice but to be strong in one direction, but not in the other, and then, if you've actually constructed T value to be non knowable. Well, then your T is non nullable, and so the normal compiler rules rules apply and so you're still gonna kind of get the best of both worlds. So.

C

How much of this do you have to know where the compiler tells you when you with whether the.

A

Compiler is gonna, generally tell you when you screw it up and basically it's gonna. If you can tell a sensitive usage, it's effectively like it's putting question marks on things, we could.

A

Like only for particular usage, you're gonna effectively see additional or fewer question marks, showing up or already associated warnings with that did.

C

He ever tried to be actually see question marks at any time, so I've led the idea. Eventually, the idea is that you'll eventually see it.

F

Mark intellisense.

C

And you'll be able to like.

F

So, for example, let's say you do try create and you put it in an F and then you reference that variable that you try to create it inside that block of the. If you hover over it and you'll, see the type and you'll say not know at this location, and then you go to the else and you use it. It'll say not with this location: big good text, yeah.

C

They'll be that'll, be in.

F

That's the current plan with the shipment 300 this football field, some of the experience is going to ship yeah, won't be refined because.

C

I was recently testing because then I could just just basically gave me the pipe that I mean.

F

I'm working on a lot of the internal pump growth, not internal the compiler side, public API- is that the ID he needs right now, yeah all right, then,.

C

Here we go then stay here. It's not generic.

A

So weak reference is one of the few where you'll see.

A

uh Yeah, so that we tweak reference is special because.

A

First, the tea is always a class, and second, we know that, no matter what tea is, if try get target returns true because of what weak reference means you're getting out non null right because it try get old target, only returns. True, if you actually had an object.

A

So it's it's not null when true and it's actually know when false, but we don't have null when false. So it's the best we can do is maybe no lintels.

E

And maybe no one false, even if you gave it creating an Austrian question mark, that's the this could be null, even though you said it should right. Correct, yeah, making sure I understand me.

C

I think this will be the feature wherever keep understanding it, as in I will understand it at some point. They will forget it and I have to we understand it again and forget it again with the end of it again. This is always going to be.

A

So in general, dictionaries don't allow null keys.

A

I, don't remember why this was needed.

E

Even if you said it was during question, work well.

F

So this is dictionary not dictionary empty.

F

People, the inputs already should be non malleable, I'm, sorry.

D

F

You're, unless there has a question in source, does it have a question source.

A

It does have a question on the return source. Oh right, this does not wait. Why is just just love? No, it's.

C

Because this is all known means, it doesn't accept the key. That is not a right. You can't pass null.

F

C

F

Signature already says right.

A

But I ye there's.

F

A question mark in source apparently return not on the top, which is wait.

E

Doesn't make because that attribute is I, don't.

C

C

You, what is this allowed? Only the other.

D

Even even if the type says he does.

E

Object and wouldn't wouldn't that then be a couldn't. This on always be a parameter or if it's an input thing, we shouldn't have it on a return, which means it shouldn't even have a method.

A

This seems like it's a mistake to me.

D

We should allow no inputs right. The only thing that we.

H

D

Allow no values, yes, I mean.

A

We allow knows, if we allowed knows, if no is a valid T value.

H

E

Is the index a right yeah, so yeah four values? Yes, the disallowed was illegal here because index Wow right.

H

This looks but saying you.

F

Can't put dollars of value into the.

E

Oh, that's trying to say no can't go in the set correct.

D

Alright, okay, that doesn't seem right. Big Bazaar attorney is renewable. Well,.

C

How did this alone now's work? Does it apply to all parameters or well.

A

It's low Nolan his position is about, though, is about the value not about the.

E

Perimeter cannot be value parameter on the center said.

C

Why is that? Because I mean basically.

E

Is that just how properties work and jam.

C

Yeah because there's.

E

No way that you can apply a parameter attribute to the value so.

H

It has to go on the I think we'd have to I, don't know if you can actually put it on the set itself. We.

A

Initially had that cuz, the way you do that is by the attribute usage target is method, but we removed that because it was deemed to be too you know permissive just say this is applies to.

C

Many said you would never want to apply to the index of parameters, because that will be weird.

A

Yeah I think we just need to remove the attribute, I think I or whoever did. This was probably thinking that you know it can return null, but the inputs shouldn't be no, but it's only that the input shouldn't be null for certain T values and therefore you don't have a way of saying that, and so we should remove it. Just so I know.

F

A

Is an implementation like like for for an implementation like dictionary of T key T value which implements this interface?

A

In some cases, you can't store null like if you, if T value is an int, the center will throw right.

E

I also comments that MSDN dogs explicitly has a paragraph saying that can be no mr. right. Yeah.

H

We just need to delete, get.

C

E

No, the tea, oh, that we might also need.

E

I think it already, there should never be knowable. What dictionary allows an open, I, don't know, but MSDN doc says it's totally like there's there's an actual sentence. It's an interface, so anything is legal. We're documenting here our belief that you should SML key because most of our dictionary.

C

C

Like a dog but to me there's no general.

E

C

E

Less the docs are written in the last year. It's probably wrong.

A

Hey, you sorry, where are you looking Unitas about the key being null lookup.

E

Of the MSD undocks 4i Dictionary dot item, not index or sub object, yet yeah, and there is a sentence at the bottom that says under remarks. Implementations can vary and whether they allow the key to be null.

A

I say I have even though, at the top, it says, argument exception. He is no. Yes,.

B

Yeah remarks are sometimes the exceptions wrong. Okay,.

E

Little here's for barians extra covariance rule. We have a complicated relationship, yeah.

A

In general, I compare and I equality compare or I compare all the compare. Things have been really hard.

F

One question about forgot: I Dictionary, the contains method did that have them aloud null or does it throw that question.

A

In check yeah in general, and we throw.

F

It does not have a question work.

H

Right and I guess my question is why.

A

Why would you pull out? Why would you allow to be No.

H

I've heard Folsom: no, it wasn't deleted. Yeah.

A

Well, that's like saying you could pass into a dictionary of string.

A

I know it's not going to contain 42 because it's strings.

F

I mean so yes, but on the other hand you have as something that is a string question mark, and then you have to check it for know yourself.

C

Well, no I think, particularly speaking on invitations, actually have the line that says, if key equals, not thought, I would know. Yeah.

E

C

Of all of our income that.

F

Contains key contains, like whoa.

G

I

G

Things value well until a key item right I mean say: that's one yeah.

A

Oh, it isn't that for set for something. What is that.

C

That would be on a.

E

Generic dictionary is.

F

He I guess I, don't know. What's line, that's actually. Yes,.

A

F

A

Right so it's like a collection of tea, so.

F

This question of string, then why and it will.

A

Because, if its collection of string, then you won't contain string, question marks sure.

F

But this just feels like an extra step, we're making the user have to do right like we, we won't throw and we will do the correct thing if you pass it all there.

C

H

Argument to flatten ulti yeah.

A

I, don't know that seems to violate the spirit of to me. That seems to violate the spirit of the whole, no ability thing if I've created a collection of non nullable things shouldn't I, get a warning if I search it for no.

A

F

To add anything to it, no.

A

But in that situation the whole point is to say is to eliminate passing nulls around and if I said this will never contain null, then I've got a program, got an error by construction searching it for no. It.

F

Seems like you, you probably got in an elevator when you didn't intend one, maybe or maybe I'm reading, sometimes some type of input from a user and I'm looking to see whether or not sure but then say argue with the plans. Right I mean that's right, I mean. Certainly today. If you search it, if you search a collection of string or now it won't throw I.

E

Hope the people issues I believe if you call dictionary string and contains, but we have ten without objection.

D

Team LM sure you.

E

Have a dictionary or the tie collection, key.

A

Moment in Flex collection of key-value pair it.

E

Also implements a collection of Tiki and I collection, T value, listen to us in relent; sorry value collection, some.

I

Reason, you don't know what it's a new we're.

E

Heating: okay, so do you don't use Dawson, Taylor I.

E

Don't know I can see the argument both ways so yeah. So new dictionary, string and Doc he's dog contains an old frozen.

E

At No that dolls, not a valid Kees, is but.

F

That's a that's. The.

E

Key collection, but it implements I collection team. It tells us.

F

So this would be a list.

E

Of string contains no heard false and not from because current allowed to the list of string, even I've got to get a list of non-billable string, as this is a compiler feature. Another one I think.

A

In case like this, we have no idea what the underlying collection supports and we have cases where it's invalid, its prominent cases where it's invalid say I.

F

Didn't realize that last part cuz I just was by if I was whole lists of the string will return false okay.

E

I'm convinced you can always write a program get into a bite of the biggest changes.

F

Well, clearly, I can't because clearly from as.

E

Has just been proven.

F

To me it is wrong, it's an interface, so both things.

E

Because the interface can't actually force this plane.

C

Alright I'm over that.

C

Maybe now my next.

A

B

A

The prototypical example of a try method with generics.

F

So long little bit design on that, it's your face.

C

Does this generally mean that anything that is generic to decide, whatever you put it alone? Knowledge is alone now on it. Generally speaking generally.

A

Speaking, although for the most part, it was the exception rather than the rule.

A

H

C

If it's possible, then right.

E

In this case, it's that weird thing the equals is covariant across no.

E

Oh but like just no know whether or not your types of we're overriding the thief.

C

You know I get what it's saying. I'm saying is more like or anything it is generic. Do we basically have to make the determination but I, think Stephen couldn't figure that that's where because you've ever really say you know if generic thing is now or not now, and do something yeah.

A

We generally don't apply our own sort of opinions on forcing something to be all it's generally just passed through the exceptions. Are things like try methods where you're in the Falls case, we have to set it to default or something like weak reference, where it's very special you know or.

D

A

Where, for whatever, for whatever reason from in the design of the thing, we basically just said, you know, no one ever pays attention to this thing being null and therefore, if you pass null it's gonna blow up and that's like to get hashcode case most of our implementations. If you pass knowable just know rough.

F

Yeah I feel like I feel like these attributes are like you, either have an interface. It's like your and only needs these attributes on try methods or you have an interface that needs it on. Basically, every method and there's not a hell. A lot in between.

C

I mean the way is the interfaces, at least these ultimately they're only tweaks right, if you have to sprinkle them very liberally and something's, really wrong.

C

And like if you look at the left-hand side like it seems like it's like more like salt and more like pepper I, guess you, salt, I, think I was about to say my girlfriend. You know everything, so it was like.

F

C

A

There are probably cases that we missed, you know, there's there's, probably a smattering of things that we missed. The way we went about. This was largely as we were going through and putting question marks and exclamation points everywhere.

A

In the initial past we kept track and comments of places where we thought we want to feel to express something with generics and couldn't and then, when the attributes came in, we basically just went back through all those comments and either deleted the comments or out of the attributes yeah, and then, if we noticed something, we did some little searching, but there are probably things that we missed and we can revise those subsequently, which.

C

Also mean there's always something that we actually use. The API is to actually see what tweaks a necessary right. Just like.

A

And in general, these attributes really just remove the need to add exclamation points, and so we would find places where we're using exclamation points more than we expected to, and we would have to go in a diet repeats either these or invent new ones.

E

When the interface like the eye, equatable as the allowing dolls and every implementer still also put those on there right, that's right, yeah.

B

H

A

If it's I believe and Fred can correct me if I'm wrong I believe if you implement it with a non-generic like, if you implement a tie, equality, compare of string, I believe for something like equals, you wouldn't have to or I start. If you did equality, compare of string, question mark I believe you could leave the attributes off because.

F

But just you'd have to keep you'd have to get the Bissell em all yes,.

B

Can happen yes, but.

H

What, if you're a value type yeah these? These are totally.

A

E

So just the battery boots are rare, except for where you have to propagate the rarity.

A

Yeah and at the moment it's it's even worse in a few very specific cases in particular, ie quality comparable with its invariance is problematic and that's currently being worked on. But right now it's the one place in our code. We actually use pound nullable disabled around all of our ie quality, comparable implementations for reference types and around everywhere. We use it as a generic constraint because of issues because.

F

The damned if you do and you're damned, if you don't.

F

C

The one it's an urn, which I get one again.

C

If not, they Stendhal ability as input exactly.

C

That method is more than just.

E

I think it has to do with some common op stuff is.

C

That unmarshal, it's all magic.

E

But it takes out their concerns. Object of get object. Value seems like there's.

F

A preparer constrained regions, no waffle, I, have.

A

The description in common says: if the value being assigned is a mutable value class than a shallow copy is returned, but otherwise the object itself is returned.

D

So the there may be no for strongbox the value saying that, even if the T is an unknown reference type in my return null because.

B

The constructor exactly.

A

This is one of the few cases we actually have a public sealed.

C

Kids are awesome, they're singing about you. Don't.

F

C

There shouldn't be mark all the as well then, following that.

F

Are we to the tuple self? Oh man.

C

It would be a massive region right somewhere.

C

Yeah, it better be.

F

Been wrong with I mean they're quite a poor little good.

C

Value to Paul's lead yeah, all I'm saying is: if you look at the difference, I mean.

A

C

A

That's a question of maybe the issue is the strongbox as a class, and so we sort of we generally have treated classes differently than strux and we've. In many cases we sort of assumed that default obstruct we just kind of ignore the fact that you can do that. Well,.

C

It's not about that. It's about the fact that you know in a video type, even if it's not constructed you know, by default of struct, it's more like the fact that you say well, they started the tougher can hold.

F

Anything right I mean here's, here's the truth. The matter is that we treat to full specialty.

E

System that tuple.

E

It does not always he hold control the other thing. So if you had a a tuple of string string, the constructor, the compiler already yelled at you, if you were letting another winter, be called people that create that's moving the boom. Well,.

F

So that's that's easy to know, which is a class and not value, to write all right.

A

There's no show to both its the value tuple case. That's the issue and we sort of ignored the default struct case and.

F

And and I mean the answer really there is that if you create a string string to bolt right fuse, if you say string string x, equals default compatible warning, we will tell you the trick that you are converting that the type of string questions print questions. It's not matched, that's not mastering yeah.

C

Basically, the idea in temples is the the you control malleability right. If you say okay me know that I can't, maybe I could say, cannot be nothing. It cannot be now yeah. The case here is that it doesn't matter what you said he's maybe now, because he specifically assigned base, if you know but yeah I.

E

Was using system that people, because, as a class.

E

It doesn't have a default constructor, you never let it only get ya.

I

B

E

A default strong to me: that's next.

A

So here we have does not return, which is relatively rare in our public surface area. It is it's probably the most common attribute we use internally. We have it on all of our leaf like a hundred of these or 300, or something of these throw helper methods, and it's on all of those.

E

That allowed null was the value parameter and set correct.

A

This was a case where you know we could have made it get, will never return.

H

Null but set allows no, so we could have made it safe.

A

Wait handle question mark and then how to maybe no on the getter or for the getter, or we could have made it safe way to handle and allowed null for the setter. And we chose this because it's pretty rare to use the setter and very common to use the getter comparatively because we wanted the types to match sort of that intent.

G

F

C

Let me do one thing because always a little crazy here.

C

C

It makes a lot more sense.

C

Hope that my life is substantially better.

G

No, but it makes at least Nelson um current is not null if value was not.

C

Yeah, let's assume you don't rip the bility just want to turn wait hold on.

B

C

B

Get back up, no, you said yes, it's for you! No.

F

Back to convert.

F

Yeah anytime, does this take into account user-defined conversions.

C

I, don't think it does I think it only handles the big source building class. That this day is this special list, a second burger. Oh, that's why I cannot go yeah yeah, the user defined conversion where I can go to go yeah like.

E

All no ability attributes was okay.

F

So the reason the reason.

E

I want is involved, it's like the.

F

The reason I ask is because user-defined conversions are this one weird place where you can accept a non null thing and return a null thing. Yeah.

E

So you could implement a convertible in return old, your heart content. We.

A

Do you could, although the you'd be violating, we have set up as the I convertible interface, but your that to string is okay.

F

So you can so you can only use basically implicitly to find conversions and something or something that uses I. Convertible and I can deliver the contract if I convertible returns model. Yes, only.

E

The implicit conversions that are defined in the language specification, yes, as opposed to user-defined Clippers. So here is my convertible. The return type most people, okay,.

F

Cool all right wanted to make sure it, because if it was just looking at you to define conversions with nothing else than you actually, then that would actually I mean you can have a broken implementation. Bro.

E

I, don't care about broken out kind of tense know if you're following the contract, so everything's fine, all right.

F

A

I I wear, at least in my experience, to have an I convertible invitation and we basically have it on all of our primitives and like one or two other types and I in other code bases I. Pretty much, never see, implementations of that yeah.

F

I mean I, think it honestly would it's going to be even rarer to be returning a nullable type from a user-defined conversion when you took a non nullable type but and you can do it and we have to account for it in the and the Rossum public API.

A

I'm excited for you of you, annotating the Rosslyn public API you're gonna have fun now.

E

Why wouldn't change type that takes a type code also be annotated with nan Olaf, nominal alien.

A

Good question cuz.

E

I'm, just looking for the implementation and I, don't see any cases where you would return mole and lesson.

C

You we would accept normal input, it.

I

A

If the type code is away know basically Richard know every.

E

Control flow that I see in that method, either returns null returns, value or attempts to call a method on value which will throw an exception.

C

But that means it doesn't have a question mark right, so you can't change. You can't call this thing of not know.

E

It does have a question mark both value and the return have a question mark in the source, but I don't see any case where it will return well, and that is intended as I see anything to make. You saying apply the same attribute because.

C

It's a positive it.

A

Stinked you're right.

B

Right so that means what is that? We.

E

Were a dog pack change? Time is again in the worst case. It will just reflect value back or else.

I

You scroll up just a tad.

I

So presumably, we also needed on the other change type overload, that takes a value in conversion type, yeah yeah, because it just.

E

Calls or a method.

A

This was probably a case where we had. We put a comment just on this overload to attend to follow-up, and then we only followed up about that over listen, yeah.

C

Beep all right now we have the do not return ones which makes sense. These are the ones that would expect that there's an O environment, it's exit, Belfast.

C

C

So does this mean you can pass it and all, but you can never retreat and all correct.

F

Instead, it's a g-string right or you turn an empty string.

F

Oh I think we, this question I went through where I go the first time.

E

C

You alright, this one, you lying on tech, sweater.

C

We were a really nearly river nose.

C

That won't notice what novel past yeah, if happens,.

E

C

Though, of course, we did.

F

That's correct: yeah I mean what are you gonna do just return. The extension answers.

F

You I those except well in the first place.

E

A-After target directory name is the same.

A

It's not actually no, no.

E

The, how is it not the first line is if path is no return or yeah.

A

But it also returns null if it's empty, if not eternal, that is effectively empty return. Nil,.

F

Not mole, if not now are MJ's I.

C

Think we talked about this earlier I think we did you.

A

So you start humors consistent.

I

C

G

Mine wasn't a sadist in this feature. You.

C

Will add 20 more attribute.

C

Not now live better to inject.

F

Not mullet came from so short.

H

Bubbles came from you.

H

C

All right that makes sense to me.

C

I mean holy making good forward for us and I want to look at this.

A

In general, all the Interop services stuff is mind-bending, because a lot of the implementations are like going to native code or they do with comm and I'm, pretty sure we have bugs throughout all this. Regarding malleability and I'm, pretty sure 99.999% of our customers won't care. I was.

C

About to say that this is also the area where there's like five people in the people using it and those people when they complain, that's all they can tell us what the correct attribution is at the.

E

Or a tracker allows them yeah if you pass an old returnable.

G

Wait, it passes melding them, so should that be maybe knowing the return yeah.

F

Should there be well we're not know, if not now that we have MELAS know something we know of no no.

A

You're, not we don't have heart know regardless would be, maybe know if maybe maybe.

C

That's so the what does it just mean that I mean shouldn't be entertained, at least that the return menu can be now.

C

It seems missing entirely right because right now we only do.

G

F

G

Are there constraints that were.

F

Like other question marks that we're missing in this diff.

E

Well, they couldn't be any way because it's generics, so the the non-generic create wrapper of type, which is a one of the generic one calls into yeah. Both the input. Oh and the return our question mark type T is, does not have a question mark. There's a method will immediately throw out there to you, but then we mean that created a prototype would also.

C

Have maybe now.

E

That should be it connected both.

C

E

Yeah, so it has a level on the input that should probably have a main one yeah, because in create wrapper type, there is, if input is more maternal.

C

That would make sense.

E

It's possible, this might be a model of nominal scenario.

A

You find what's in what it is.

I

I'm trying to say.

B

Kind of all the.

H

E

I'm just I'm looking at the the generic create rapper of Titan, and then it calls into the non generic one and I'm just trying to trace the flow there. But this is another case where I don't see a scenario where it returns null unless the original input.

A

Yeah I'm just trying to see where it might return null, even if T rapper.

A

Yeah no I think you're right. It should probably be.

A

Maybe now, on the result.

C

It does not now, if not null imply that if the input.

C

C

Let's say the input is now that the output is also known. I, guess it does right. It.

A

Does it doesn't necessarily imply that it.

C

A

Does not it only it all, you can all it only guarantees that if the input is non, no the result will be nothing, but the input could be no on. The output could still be non.

C

But then, basically both of them could be applied right, depending on how we deal with their input either. Maybe not.

H

A

You I also don't know enough about the implementation, especially when it calls off into the run time to make.

E

That guarantee yeah, maybe maybe Jeremy, would be the best person to that's, but I am looking through the runtime code and I see uh it looks like it prefers to throw an exception rather than return null. But talking about my way.

B

It probably does both depend.

C

B

C

Depending on which cooperating.

C

And I guess get committed, faithful object is yeah counter turn now yeah.

B

Yeah make sense.

E

A

My guess is we, my guess, is we follow that through and found that the run time through an exception, if always past it.

E

Is the idea that disallowed mole on the parameter allows you to pass string question mark as the T without getting a compiler error? You.

C

Know why wouldn t not constrain the team to be not know if.

E

You have a caller that itself is not constrained that would no source break.

F

C

A little Houston.

F

Into question I.

C

See because they're the generic constraints of our own.

C

Well, I guess when the most party would not be in the generic context, I suppose, but yeah.

C

That's unfortunate right if it would be in any way, if you I will probably constraint it either way, it's only because it's an existing, if you know it depends on what they want to be able to pass in question. Well, if the only usage of the T this alone now, why would you allow it.

E

You I don't think it would make sense to ever pass a struck to type there, because, what's going to happen, is the value that you pass in copy front? It's going to be boxed and then you're going to get back a basically a Kong pointer to the object that is now boxed that you don't have the original reference. Well.

C

But not know doesn't imply, that's constrain. Does it itself.

F

Does not imply faster.

C

It just says that if it's, if it's a class, then it can't be no. No.

E

I guess what I'm I guess? The point of me saying that was like ideally get calm interface for object would have had where T is non-volatile. Yes, but that would.

C

I guess all I'm finding is to meet this alone now, if there's only one usage of the generic itself themes at that point, you can either decide to mark the team not null or to put the attribute right there. Basically, what.

F

It wouldn't be we're a non Melville class because instructors.

E

Can implement interfaces yes, but it doesn't make sense to get a comm interface for a struct that you're about to convey by value. You can't do anything useful.

E

I mean you, you could technically do it, but the scenario is just nonsensical.

C

Yeah I mean commenter of instruction to say not inconceivable, but.

A

Anyway, and in general for these one-offs, we opted not especially these kind of nice things we opted to just use. The simplest thing of disallowed know.

G

A

Than constraining because constraining to not to call- and you know not null as I- think Levi or you know, I was saying you know it does mean that if you are in a generic context, someone else is getting your tea. Now you have to deal with suppressing warnings from that not having been constrained. This is sort of the most permissive all still achieving what we want.

C

And with the design space right for that new API is, you could probably do? One of these I mean.

A

Even for some existing things where it was like a big impact, we still locked over the constraint like dictionaries. Tiki is constrained to not know, but the alternative would be to have disallowed null everywhere. Tiki appears yeah and that doesn't flow well through some of the resulting kind of you know things like getting the enumerator from the dictionary and stuff like that. Those.

C

Things also generally save beds right because it would have never.

E

Is if I did have a rapper that had to call a method like this? In my own code is suppression just a matter of putting the explanation on the generic crime in.

A

In most cases, you can use an exclamation point, putting it on the generic type parameters. One case you can't I, don't know I meant it remember like in some cases you you, the only option is to either disable nullable or fall back to a pragma warning disabled, but.

E

There there are workarounds, even if they're on their.

A

Rapidly absolutely are workarounds you easily just need to suppress it. It's just a question of how how many characters is the suppression from, and it varies from one for the exclamation point to like you know, thirty for a pragma, learning-disabled, bla yeah.

E

And, of course, once you disable crowd when you have to remember to turn it back on.

C

So this alone, now alone, are for this guy.

C

B

B

B

E

Is one marked, maybe Knoll? Oh it's one returns to.

B

Because water turns and Tina when he comes down PDR.

E

E

C

C

Mean happy baby eyes you're like you're, okay, why? Whatever baby.

E

So, what's that will tell us when we get it wrong, wouldn't get objects for native variants, be the same thing we're in you're returning a tra, but those individual T's could potentially be no and.

C

I think we can express that. Okay, and this is what this case you would be able to put a question mark right said. Presumably this one would be object question my record record right, yeah.

E

So be the non-generic one returns an object. Question mark brackets, like you said, a non-generic whenever eternity question mark because I'm like yeah, we.

C

Don't even attribute.

E

That I don't have any I, see the element.

C

Of an array like we.

E

Don't know we don't have an actual nest availability. Is there potentially an attribute that just says suppressed no mobility on this API in general, because we can't express what we're into.

F

That would that would be called just fragment disabled yeah. We.

E

Know, kids API it could be Kyle.

F

How many of them all.

E

Different movies, so you would so you would prefer for the caller to do the suppression rather than for us to make.

C

Yeah, when you define the API, you can basically say malleable disabled around the type. If you want to be oblivious which base in Indonesia. No, no, no, no, not.

E

Does it make sense for us to have such a declaration around these methods that we know we can't quite correct? That's.

C

An interesting point I think that that might actually be not a bad idea. I mean it I guess it depends on what you optimizing for and if you give, if you have a spread 50-50 between courts, positives and false negatives, and yes, if it's more like 80 percent, is correct and your 20% false positives, and maybe that's over the board right well,.

A

I mean I miss mr. suggestion. What was the.

F

Suggestion would be to potentially surround get objects, coordinated variants of T with.

E

A with a nullable.

F

Disable an honorable and middle because we can't express the nest availability on the on the array of th, but I. Don't think that would help honestly, because so what does? What does making it oblivious do? It just means you won't get warnings about it when you treat it as null or.

E

Treated is not not the two.

F

People in the world who uses API so it doesn't it doesn't by the user or anything I, don't think.

A

Have tried really hard for better or worse, not to use notable disabled for and I think we we added about fifty of them when we did the like equality, comparable thing, but we should probably you know if.

E

We want to start.

A

Using it more liberally, we shouldn't think hard about it. Well,.

E

The reason I bring it up is because potentially if we do find the ability to expresses in the future- and we do change the API to have the new attribute when it comes up- that would be a source breaking change, correct which may be wrong hailing. It just wanted us to make sure that, yes, we're not getting into a corner yeah.

C

I'm not sure we won't get to the notification, because then, and at that point you're ending up the you know the design space gets complicated fans from their own okay.

C

D

C

Maybe now until hundreds of structure.

C

C

Wouldn't there be not pull the inputs, oven pointer, oh, we can expect.

C

C

This is all knowledge should be.

C

Alright, that makes sense.

C

I'm actually making forward forward.

G

Oh, that's easy.

C

That means because you can never set it now, but you can retrieve it now.

F

C

It does seem odd.

C

We sure that's right.

F

Well, so it doesn't have a like that says anything in the constructor because it doesn't take a parameter. So if you want to set something said it don't want to set something get whatever the default is.

A

But if you wanted to be able to set it to know, you would use a nullable t. Oh no, actually the T is constrained to be class.

A

I

A

The way this is the way this is set up, we're basically saying you don't store nulls into this, but.

F

Because because it doesn't have a default value anywhere, you could get in a lot if you haven't for anything yet so.

A

The question is: do do we actually want to allow you to store.

E

Well, it looks like the behavior is setting it to mole is equivalent to calling clear yes.

F

Well and then, in that case, you probably do want to allow you to set know if we're handling it, which.

A

Would mean changing.

H

That would mean adding.

F

H

A

Or or or changing event registration, token table of t where t : class to be t :.

F

Because then, if you made it, then if you made an event registration token, a string, then you wouldn't be able to use that functionality. Why not just make a vacation was to work and leave the class yeah.

D

This is pretty question mark because, since it is constrained to class yeah.

F

And you can just put t question.

C

That make sense me I, guess.

A

I'm well hold on, like.

F

A

Are other places in the implementations where TV all is supported, like look at event handler an event handler says if handler is null return, new event, registration, token of zero, but.

C

Wouldn't say if you're constrained to class shouldn't be generally not saved by default. You put the question marks all the time.

A

Saying if you aren't doing it so.

C

I'm saying we're.

A

Gonna allow those here shouldn't it be. Where t : class question marks, they said if you want to use them to know. If you want to support null, you use unknowable, T right.

F

But my point there Stephen is that invocation like like the return of invocation list. If it was class question you still need, then maybe null attribute, and you still need that. Allow not review there, because what do you do about No yeah? You would because if you.

H

B

F

If you want to be able to set null and it even because it was.

A

F

With string, don't.

A

Do that that's like saying: I want to be able to use the string question marks in a dictionary event string then I should have declared it as a dictionary event string question mark.

F

And yes, but we were the thing with with invocation the sending it to not right was that it was the side-effect of effectively calling clear on this thing yeah. So it's not necessarily right. It you're doing that for the side effect of the thing and you're not doing for.

H

Them this thing is basically a delegate.

E

Right there is an ADD method which is combined, there's a remove method and there's no clear method and because there's no clear method, the equivalent of a clear method is but.

C

More philosophically I think I think the even suggestion makes sense if all usages of the tea in the class would accept now all the time for now an eternity which I'm not sure as the problems you would make a point. It makes more sense to me to say where t : class and then just put the question marks at the only API where you happen to support nowadays, which today might be everywhere right. But is that true for like for eternity and is that the promise you wanna make.

C

That seems more logical to me, like you wanna, you want to indicate the areas where you alone now, rather than University, saying for this type. T can be no I. Think.

A

There are, there are two issues here: one is I think are where t : class is wrong, because you just look at the public API like it's valid, to pass null yeah to everywhere, and the public API surface area that accepts a T yeah. Okay, on top of that, Fred is saying, and Levi is saying they believe that, even if you use an on nullable T, you should be able to pass a null to invocation list right, I'm, not sure I, agree, but I understand what they're coming from.

E

If we didn't have that than we should, we should at least introduce or something well, we should just tell people if you want to clear.

F

And you would need a maybe no activity on that still because if you don't say it, you.

H

A

Strongly about it, we can add a allow, no I'm, fine with it. I just I mean.

F

I, don't I don't feel super strongly about it. I just I'm wondering whether or not people will use this for the side effect. We could always not add it to start with, and then, if people complain, we can add it. What I don't understand is like what kind of but like. Why would we put the attitude with rather than putting a question mark on the teeth? Well, because we're saying because you were your question about, do we guarantee that this thing will always accept nulls.

G

And what's the class.

F

I'm saying like knowing it's public key cuenta, making.

G

Location would know so I'm, saying I'm, saying your earlier surf. You construe the last question mark you can add a question mark to the tee, but even if you can spread into clouds, you can't no, you can't. If you can straight it's a class, but not straight. It's classic question right. So what I'm.

C

Saying is, instead of doing attributes and not putting a question right behind the class key, where we can also put a question mark just behind the team before education. This.

A

We clean where to go in class, then everywhere we use tea in a public API. We could change it to tea question work.

F

Right so the question is: should we just allow it to be questions if we just allow it to be last question, certainly because anywhere did you have enough like again.

C

I guess what I'm asking is like you would like you would go all I'm saying is that in this particular class it makes no sense for me to use attributes, because you either put a question mark or you put either you put the question marks at all usages of T or you put it in the generic constraint, but whatever you have to get in this class, so.

A

If so, so, there's there's a few cases here, we can leave it at. We can leave it as it currently is where we have, where t : class, we have attributes on in an invocation list and potentially attributes on other public api's that accept T. If we don't add the attributes elsewhere, then currently we're Sybase is saying no is not accepted, so things like add event handler, there's the option of changing where t : class to be where t : question mark, but then to your question emo.

A

If someone constructed that with a non nullable, T, Fred and levi's argument, as you still use, you still need the maybe not on invocation list, even where T is constrained to class question mark, because we might still return null. Even if someone used an unknowable, T and then there's the third option which, as we say where T : class and everywhere we use T in the public API. We then use T question mark, in which point we can remove the attributes.

A

C

But even if you say the last option, it doesn't have to mean everywhere I just you could still pick and choose right.

G

F

Good point: the point is that every single one of these API is public API sandals, not right.

C

I guess I guess my question is more is more pointed towards just ignore this particular class instance, but this particular instance of this class, where, when you have it C that is constrained to class, why would.

F

I ever use attributes because perhaps let let's say the original definition of this thing, you can never set invocation list to a malleable value, but it starts off with a default. That is normal right. There's, no way to express that this has different in and Algerian swith, except with an attribute right. If I give you if it's--if is a symmetric.

A

Which is exactly why there's a maybe not on it right now, right.

C

Would put alone, and maybe not any might as well just put the question mark Christ unless.

G

You literally can't they're expensive, so.

C

What do we should we do here.

A

I think we should not leave it. The way it currently is.

B

A

Hard stance I think unless, unless there's I think we should just change, we should remove the attributes and change the t's to be in the public API to be T question.

F

Okay, business yeah.

H

If the constraint does, where t : class.

F

Registration token table is used for, like so I. Don't I, don't know if instantiating with a screen question mark is the thing that someone would want to do. Bird composability so.

E

It's it's a delegate like you, the T is a delegate.

F

Well, I'm not going back with me how well I mean so that is, it can but like.

E

F

E

Basically, a glorified play, it's a glorified call, a double get talking line and don't.

C

E

A

We wanted to make it where t : class question mark then I think we would add a low null on every T input and maybe now on every T output.

C

Interesting I guess that's true right! Even if you put a question mark at the constraints, you can still widen it afterwards with the attribute.

E

I seen a lot of places where invocation list has read that never where it's set I'm looking through this way, I believe this is done with a compiler. This compiler cooked before these I'm, the code I'm looking at is all code. Those written by humans, yeah.

C

What I'm saying is that it mean it I think the registration token table I believe is used when you implement a interface instead, oh yeah, and then in the compiler item. It's coded this without you, but you might be right that even the complainant, my name is well.

E

C

Not have visibility into.

C

All right, so then this is that we have 10 minutes left, which means you might be able to do. 10 more files. There were two cookies left. ah I pressed my whole quitting might actually succeed in Freddy.

F

Depends on how many of these we take off its you.

D

Come from one cookie to stephan1 to me, I can try.

H

F

No but then they're not my cookies.

B

Make sense actually get a blowout.

C

You, oh, why are we doing this here? Didn't we say the donkey on star.

C

A

We don't care for default, but this isn't the default case Oh like when, where the context changes there may not have been a previous value. Let's say my kid: No.

C

E

F

C

Chris, better and.

A

So yeah so exchange is an interesting one where both the return and the first parameter, the ref parameter, are not null, if not null. If the second parameter is not null.

C

Yes, you guys, we think it would be fun, no I, think exchange.

E

C

E

Returns the original value.

A

E

A

That's for that would be for right, dis for exchange.

A

Exchange that should be on the result. Yeah.

F

It should only be on the first parameter well,.

A

Actually, no, it should be on the result, but it should be or location one salt, so.

E

I'm I'm a little confused because it when you call me I, don't exchange you're generally going to point to like a field instead of a local variable, something like that which means at the time exchange, returns and says. Yeah I said a dog no value there as soon as you try to dereference it in the line immediately thereafter, it could be no again so.

A

It threading is entirely not factored in for no the no ability stuff like that's true, even you know, property reads like the compiler assumes that a property's, no ability doesn't change from call to call, but obviously even threading aside. That's not true.

H

So when there's a bug here.

A

But it's the like, so exchange the the location. One will be not null upon completion if value was not null and the result will be non null upon completion if the location was not so the duck. The those results should be of location, one, not a value.

A

This just a copy-paste, our.

F

B

That Super Bowl.

C

B

E

Whispers heritage in there sorry.

A

The compare exchange is so complicated. We don't have an attribute to express it at. My hope is the compiler is going to special taste. It.

B

There's no way if you've never used, exchange I think they only ever use yes exchange once I can use.

C

Oh very cool: well maybe.

F

We have not now target that next time, when we should live, not wait. Why are some of them.

H

Aloud Mel and some of them not know what was that right, so there.

A

Are multiple overloads here that fall into two buckets one of the buckets they just work with reference types and are typically used if you're just initializing some reference fields from not from null to nominal. The other overloads can work with any T, struct or class and as a result, since they can't use. You know whether it's null or not, to indicate whether it's been initialized or not.

A

It has a bool initialized field as well as an object that it uses as a synchronization object and does double check, locking and those two buckets that end up with different semantics around the null ability of the T.

C

Can you explain to it with the differences between not not actually didn't disallow, no actually.

H

A

Ears on the way out, disallow us on the way in.

F

Allow and disallow our inputs and then the other two are updates yeah. So it's when it when the method returns, ref target will not be known for those yeah there's no way other factors.

E

That actually matter, to be honest, oh just about matter, because generally the way that people use things like insurers realized is this Assam ref to some field into this API, which Everly tends to be the only place where that field has ever used inside your entire code names generally. What you do is you call it sure, initialized read the return value and then use that, rather than looking at the particular case. Maybe.

C

Sometimes, but.

A

There are also a bunch of paces for people just to ensure initialize like at the beginning of their method, and then they'll use that thing they'll use the same field later in the method. Knowing that previously, it had been initialized quick.

F

Question is these: are these actually constrained to where T is class question and we're just not seeing the question.

F

Okay, then, why do they have not known on the output if they're already guaranteed to be Class C? No.

A

Because the the ref t target is actually ref t question target. Okay,.

F

That's what I think you I knew. There was a question somewhere that I was missing. Yeah.

H

A

Is hard without seeing the question works, yeah.

F

B

F

What the rep target part is now what were the other attributes from this thing, with the other teeth? There's the only other parameters, there's not no for the simple okay.

D

A

I go ahead. Sorry for.

D

The ones that take his truck shouldn't, we have a nap I'll put attribute as well in the raft target saying no, we.

A

Can't because II.

A

It's possible that they could be used to initialize tea, to know.

F

I mean if you have a string question, if you, if you use green question, that value factory could just return that if.

E

You so for things like value, factory of birth or api's, without initialized or a sink walk, you know is not valid from a usage scenario, because I'm sure initialize will get called over and over and over and over again, so just yeah. So if, if you're looking at this overload market system value factory, if you, if this value country memories mailmouse they're going so if this value factory here returns old, every single call to ensure you.

F

Put the mouse cursor, so they know so that people are gonna.

E

Know is support why this one yeah, this factory returns an old every single call to ensure initialize to a cold effect. So.

A

Value factory returns, don't we throw an exception? Okay,.

A

In that overload, he wants to take an object, anything's, fair.

F

H

We had to stare at these for a while.

B

A

One of the interesting things about this whole novel ability effort is it it well absolutely have an impact on how I think about API design in the future, because the more complicated the API, the more you need to stare at these apps and I, don't want to stare at these attributes so I'm, all for really simple API is even more so than we already tried.

F

I'm, not what you, okay, yeah,.

F

A

And again, and all these that I believe there's a question mark on those out.

F

F

On the default constructor, you.

A

Every threat, if you just use the default constructor every thread that accesses that, but not having been set, will be no.

C

We so we have winning them.

C

C

Finish this one you and then we have basically done all Sony everything below.

C

C

F

Oh yeah, okay, so if you were, if you write value to objects or to address them.

B

Our teeth dead, so it's popular so what's left is these five.

C

Which means giving the velocity we had probably an hour seems reasonable.

F

A

Long as you don't spend another hour getting the diff working, yes,.

C

Well, no I know no I, have it already I, just double-click right, don't.

H

Restart your machine.

F

Or, on the other hand, you couldn't make the viewer actually work and and stop asking Oh. Is there a question mark on this invoice.

C

Yes, we should probably just make sure to work at this one anyway. Okay, that was there another meeting for tomorrow and probably and then we should be good to go all right.

C

Nobody disagrees with me, so I think this is a resounding assurance that that is right and then I will sign off now. Bye-Bye.