[swift-evolution] The bind thread

[Howard Lovatt]

I like this proposal. I also think that either bind or exists could be the
keyword. I would suggest that both forms of syntax should be allowed, e.g.:

    if bind x { /* x is non-nil, unwrapped, and hides original x inside if
statement */ }
    if bind x = object.property { /* x is non-nil and unwrapped */ }

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

> 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
> <javascript:_e(%7B%7D,'cvml','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
> <javascript:_e(%7B%7D,'cvml','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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-- 
  -- Howard.
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