[swift-evolution] The bind thread

[T.J. Usiyan]

I didn't actually try
```
if x? {
foo(x) // x type narrowed after binding.
}
```

in a swift file and I should have.


To misquote a movie
*That code, you keep using that code. I do not think it does what you think
it does.*

I *do* recall discussion of this syntax and it might have been in an
earlier version, but it does not work now. What I receive is  `error:
optional type '_?' cannot be used as a boolean; test for '!= nil' instead`.
I agree with this because that question mark was not, in my opinion, sigil
enough for the action.



On Mon, Feb 1, 2016 at 2:56 PM, Tyler Cloutier via swift-evolution <
swift-evolution at swift.org> wrote:

> The bind or exists keywords seem sort of silly to me. There is already
> syntax for binding optionals:
>
> if x? {
> foo(x) // x type narrowed after binding.
> }
>
> Tyler
>
>
> On Feb 1, 2016, at 11:35 AM, Howard Lovatt via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> 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> 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> 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
>>>
>>>
>>>
>>> _______________________________________________
>>> swift-evolution mailing list
>>> swift-evolution at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>
>>>
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>>
>>
>
> --
>   -- Howard.
>
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