Remove ^ in capture set syntax #22725
Conversation
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Let's rebase this on #22539 and wait until after the release cutoff before merging. |
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I don't think we need to rebase onto the separation checking PR. The change here is only inside the Typer and should be independent to the core cc phase. |
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How about all the test cases that need to be updated? I think it's better to rebase. |
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This scheme has the advantage that the code is very simple. But there is an issue: Assume we have object C
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def foo[C^](x: A^{C}) = ...then A^{C} will refer to the outer val C: Capability = ...then we get scope inversion. The outer C will be selected over the inner C. I think we should try to avoid these problems by using a scheme similar to CBCompanion where when we run the Namer on |
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I see, if we keep searching terms first, we need to create a "fake" symbol for every type bounded by |
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I need to wait for the syntax change in #22758, so it is easier to tell which type def is a capture variable. |
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I agree. I first thought this was independent of the syntax changes, but maybe that's not the case. |
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@noti0na1 it's fairly complete now, modulo adapting the test cases. |
…#23063) Closes #22490 Builds on #22725 Supersedes #22902 This syntax for capture variables and members caters to the view that "they are another kind", and most conventions we know from higher-kinded type parameters carry over. A postfix `^` (analogous to `[_]`) indicates that a type parameter/member ranges over capture sets ```scala def sayHi[C^](l: Logger^{C}) = l.log("hello world") trait LList[T, C^]: type D^ >: C // or equivalently >: {C} val node: Ref[T^{D}]^ ``` These variables can be bounded by capture-set literals: ```scala trait Foo: type C^ type D^ >: {logger} <: {logger, async, this.C} type E^ : Monad // error, context bounds are forbidden ``` Just as with higher-kinded type parameters, the kind is "contagious", and we can often avoid the hat if the bounds are concrete capture sets or other capture variables: ```scala trait Foo: type C >: {} <: {cap} // no hat needed type D >: C // dito type E = {x,y,z} // dito type F >: Object <: {cap} // error, ill-kinded ``` Capture variables will be erased if capture checking is turned off. In non-capture-checked code, they are essentially type variables within the interval `>: caps.CapSet <: caps.CapSet`. With capture checking turned on and without explicit bounds, the interval corresponds to `>: caps.CapSet^{} <: caps.CapSet^{caps.cap}`. ## Tasks - [x] Bullet-proof the "can avoid the hat" for binders scheme. - [x] Grammar doc. - [x] Update language reference. - [x] Port new tests. - [x] Clarify when and where to produce attachments. - [x] Forbid nonsense intervals mixing capture sets and types.
This PR simplifies the capture set syntax by removing unnecessary
^symbols in capture sets.This change is the first step making the syntax cleaner and more consistent for capture polymorphism.
InCaptureSetmode inMode.scalato handle capture set annotation typing;^suffix from capture set syntaxInCaptureSetis set and a term ident or select is not found, retry typing as a type wrapped inCapsOf.