[swift-evolution] Fw: Re: [Proposal Draft] Literal Syntax Protocols

Adrian Zubarev adrian.zubarev at devandartist.com
Fri Jun 24 10:41:15 CDT 2016

That said, how about this design:

public protocol _LiteralNilProtocol { … }

public enum Literal {
    public typealias NilProtocol = …
extension Array: Literal.ArrayProtocol  

Adrian Zubarev
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Am 24. Juni 2016 um 17:37:27, Adrian Zubarev (adrian.zubarev at devandartist.com) schrieb:

Really? I must have overlooked that some pitched that design.

Okay now that I think through this whole scenario, I like the underscore iff there is a good name that will be present in the final version.

When Swift 3 drops, I’ll write a proposal for nested protocols which will refine your design (the original author went missing after pitching this idea, and Joe Groff told me that this probably out of scope for Swift 3)!

Your current design might become this in Swift 3.X and all protocols marked with an underscore will disappear:

public /* closed */ enum Syntax {
  public protocol NilLiteral { ... }
  public protocol BooleanLiteral { ... }
  public protocol IntegerLiteral { ... }
  public protocol FloatLiteral { ... }
  public protocol UnicodeScalarLiteral { ... }
  public protocol ExtendedGraphemeClusterLiteral { ... }
  public protocol StringLiteralLiteral { ... }
  public protocol StringInterplolationLiteral { ... }
  public protocol ArrayrLiteral { ... }
  public protocol DictionaryLiteral { ... }

Adrian Zubarev
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Am 24. Juni 2016 um 17:25:45, Matthew Johnson (matthew at anandabits.com) schrieb:

The design in this proposal comes from the standard library team.  The intent is for the use of underscore here to be consistent with other uses of underscore prefix in the standard library.  I’m not sure why you think this is different than the rest...

On Jun 24, 2016, at 10:22 AM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:

I’m aware of that fact, but all types with underscore even in the stdlib telling me to keep my hands of them, because something might happen to them.

As an example we have _Strideable protocol which is visible by its name, but its declaration isn’t visible at all:
// FIXME(ABI)(compiler limitation): Remove `_Strideable`.
// WORKAROUND rdar://25214598 - should be:
// protocol Strideable : Comparable {...}

% for Self in ['_Strideable', 'Strideable']:
From Stride.swift.gyb

Adrian Zubarev
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Am 24. Juni 2016 um 17:09:53, Matthew Johnson (matthew at anandabits.com) schrieb:

The underscore is used in the same way it is used elsewhere in the standard library.  The protocols must be public because they need to be visible to user code in order for the design to work correctly.  However, they are considered implementation details that users really shouldn’t know about.  This pattern is well established in the standard library.

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