[swift-evolution] The bind thread

Andrew Bennett cacoyi at gmail.com
Mon Feb 1 18:49:43 CST 2016

I mostly agree with everything you said. I also think "if case" syntax is
bad at the moment.

However I think any changes probably have to be an addition rather than a

I've tried to reconcile these changes with pattern matching and cannot work
out how it fits. There's too many inconsistencies and incompatibilities. At
best you can make a new pattern matching syntax that's incompatible with
switch statements.

On Tuesday, 2 February 2016, Brent Royal-Gordon via swift-evolution <
swift-evolution at swift.org> wrote:

> >   if bind foo {
> >       // foo is non-optional in here
> >   }
> If something in a flow control statement should read like an assertion, we
> don't want "bind" here.
>         if has foo {
>                 // foo is non-optional
>         }
> However, I do note that pattern matching in an if statement already lets
> you do the same thing as `if let` more explicitly:
>         if case let foo? = bar {
>         }
> I wonder if we should instead enhance this feature's usability. For
> instance, as a surgical change, we could drop the `case` keyword when `let`
> is present in the condition (since `let` isn't allowed in a boolean
> expression anyway):
>         if let foo? = bar {
>         }
> This is one character longer than the current `if let`, but it falls
> naturally out of other language features and allows for other similar
> constructs, like `if let .Success(value) = bar`.
> However, the `if case` syntax kind of sucks in other ways, too, and I
> think it deserves another look. In particular, the `=` isn't great for
> pattern matching that doesn't bind variables; people have complained about
> that part of `if case` before. Maybe we can improve that while still making
> the unwrapping good by introducing a keyword or operator that replaces the
> `=` while implying the `case` so it doesn't have to be stated explicitly.
> Here's a strawman of what this would look like, using `matches`:
>         if let foo? matches bar
>         if let .Success(value) matches bar
>         if .Card(let rank, .Heart) matches bar
>         if .OK matches bar
> Can we do this with `for case` too? Maybe...
>         for let foo? matches in bars
>         for let .Success(value) matches in bars
>         for .Card(let rank, .Heart) matches in bars
>         for .OK matches in bars
> I think this approach might work; the only question is what `matches`
> should be. I don't like using a keyword for it; I think it disappears too
> easily, particularly in the optional case. We do sort of have a pattern
> matching operator, `~=`, but it's very obscure, the overloading is not
> really right, and I can never remember which order the characters go in
> (possibly because Perl uses `=~` as its matching operator). Colon kind of
> reads well, but it disappears too easily, and it's already associated with
> typing:
>         if let foo?: bar
>         if let .Success(value): bar
>         if .Card(let rank, .Heart): bar
>         if .OK: bar
> I don't know what the answer is here, but I think this might be a good
> line to pursue.
> --
> Brent Royal-Gordon
> Architechies
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
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