[swift-evolution] The bind thread

[davesweeris at mac.com]

I think it’d be _

You could use it to test if the return value is non-nil, but you’d have to revert to “if let x = …” to actually use the results.

I think.

- Dave Sweeris

> On Feb 1, 2016, at 11:22, T.J. Usiyan via swift-evolution <swift-evolution at swift.org> wrote:
> 
> This is interesting. What name is created by 
> 
>   if bind foo.somethingReturningAnOptional {
>       // ???
>   }
> 
> On Mon, Feb 1, 2016 at 2:18 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Joe says "If you all are serious about this, I think you should start a new thread about it." 
> I think it's worth a serious discussion just so it can be evaluated and either adopted or discarded
> and dropped forever. Here goes.
> 
> INTRO
> 
> The if let x = x {...} and guard let x = x else {...} constructs do something with let (and var) that's 
> fundamentally different from let (and var) elsewhere in the language.  The same keywords are used to conditionally unwrap
> and bind an item, not just shadow that item's current value.
> 
> Introducing a new bind keyword to indicate unwrapping and binding would disambiguate these uses.
> 
> DETAIL DESIGN:
> 
> Jacob Bandes-Storch offers two common use-cases. I prefer his "if bind foo" to my original "if bind foo = foo":
> 
>   if bind foo {
>       // foo is non-optional in here
>   }
> 
>   somethingAsync { [weak self] in
>       guard bind self else { return }
>       // ...
>   }
> 
> JBS's approach offers my original "bind" keyword to unwrap and shadow bind, but also provides a way to 
> strongly bind a weak reference to self, which (presumably) would allow self semantics in the remaining
> lifetime of that scope.
> 
> ALTERNATIVE PROPOSALS:
> 
> Tino Heth proposes a second use-case one with different semantics. This case, it seems to make an
> alias rather than using binding for shadowing:
> 
> bind x = a.property.with.a.long.path
> print x  // 42
> print(a.property.with.a.long.path == 42) => true
> 
> presumably this means:
> 
> x += 1
> print(a.property.with.a.long.path)  // 43
> 
> DISCUSSION
> 
> I'm throwing these both out there. I have nothing to really say about Tino's but I do think my and Jacob's 
> proposal has the advantages of:
> 
> * Simplifying an mildly complex and potentially misleading statement 
> * Creating a deliberate and controlled rather than accidental shadowing style
> 
> Have at it.
> 
> -- Erica
> 
> 
> 
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