> Le 15 août 2016 à 10:01, Justin Jia via swift-evolution
> <[email protected]> a écrit :
>
>
>> On Aug 15, 2016, at 3:53 PM, Charlie Monroe <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>>>
>>> On Aug 15, 2016, at 9:46 AM, Justin Jia via swift-evolution
>>> <[email protected] <mailto:[email protected]>> wrote:
>>>
>>> I think the `?` will make the return an optional. So your example should
>>> add another ? at the end.
>>>
>>> ```
>>> print(foo(bar(42)?, baz(42)?)?)
>>
>> This reads terribly, IMHO.
>>
>
> I agree that this reads terribly. But this is only an edge case. I would
> prefer `let output = foo(bar(42)?, baz(42)?); print(output?)`. However, I
> want to argue that for most cases “?” reads better than “if let”.
>
>>> ```
>>>
>>> The above example should be equivalent to:
>>>
>>> ```
>>> let x = bar(42) // X is optional
>>> let y = baz(42) // Y is optional
>>>
>>> let z = foo(x?, y?) // Z should be optional now
>>> print(z?)
>>> ```
>>>
>>> which should be equivalent to;
>>>
>>> ```
>>> let x = bar(42)
>>> let y = baz(42)
>>>
>>> if let x = x, let y = y {
>>> z = foo(x, y)
>>> }
>>
>> What if baz doesn't return optional?
>>
>
> If baz doesn’t return optional, then we don’t even need this syntax:
>
> We can just write: `z(bar(42)?, baz(42)` and treat baz(42) like normal.
>
> Which should be equivalent to:
>
> ```
> ```
> let x = bar(42)
> let y = baz(42)
>
> if let x = x {
> z = foo(x, y)
> }
> ```
>
It is not consistent which what I expect when calling foo?.bar(baz(42))
In that case, if foo is nil, bad is never evaluated.
>> if let x = bar(42) {
>> let y = baz(42)
>> z = foo(x, y)
>> }
>>
>> or
>>
>> let y = baz(42)
>> if let x = bar(42) {
>> z = foo(x, y)
>> }
>>
>>
>> If both are evaluated, this is really inconsistent with
>>
>> if let x = bar(42), y = baz(42) { ... }
>>
>> which will short-circuit and baz will not be evaluated if x is evaluated as
>> nil.
>>
>>>
>>> if let z = z {
>>> print(z)
>>> }
>>> ```
>>>
>>> We don’t need to worry about “short-circuit” now because it should be
>>> equivalent to the above syntax.
>>>
>>> > It has been mentioned before (more than once, perhaps, but not in its own
>>> > thread I don't think, so good luck finding it). IIRC, one of the problems
>>> > is that it's unclear what happens if your function takes multiple
>>> > arguments. Does evaluation proceed from left to right? does it
>>> > short-circuit? Put concretely:
>>> >
>>> > ```
>>> > func bar(_ x: Int) ->Int? { /* side effects */ }
>>> > func baz(_ y: Int) ->Int? { /* side effects */ }
>>> > func foo(_ z: Int, _ a: Int) ->Int { /* ... */ }
>>> >
>>> > print(foo(bar(42)?, baz(42)?))
>>> > ```
>>> >
>>> > Does baz(42) get evaluated if bar returns nil? Does bar(42) get evaluated
>>> > if baz returns nil?
>>> >
>>> >
>>> > On Mon, Aug 15, 2016 at 2:02 AM, Justin Jia via
>>> > swift-evolution<[email protected]
>>> > <mailto:[email protected]>(mailto:[email protected]
>>> > <mailto:[email protected]>)>wrote:
>>> > > Hi!
>>> > >
>>> > > I don’t know if this has came up before. I tried to search though the
>>> > > mailing list but didn’t find any related threads.
>>> > >
>>> > > This is purely a syntactic thing (which I know it’s the lowest priority
>>> > > for Swift 4), but I think it’s an important one.
>>> > >
>>> > > Let’s say we have a struct with a function:
>>> > >
>>> > > ```
>>> > > struct Foo {
>>> > > func bar(x: Int)
>>> > > }
>>> > > ```
>>> > >
>>> > > We can use optionals:
>>> > >
>>> > > ```
>>> > > let foo: Foo? = nil
>>> > > let x = 1
>>> > > foo!.bar(x: x) // Able to compile, but will cause runtime error
>>> > > foo?.bar(x: x) // Able to compile, and won't cause runtime error
>>> > > ```
>>> > >
>>> > > However:
>>> > >
>>> > > ```
>>> > > let foo = Foo()
>>> > > let x: Int? = nil
>>> > > foo.bar(x: x!) // Able to compile, but will cause runtime error
>>> > > foo.bar(x: x?) // Won't compile
>>> > > ```
>>> > >
>>> > > I propose that we should allow `foo.bar(x: x?)`, which should be
>>> > > equivalent to:
>>> > >
>>> > > ```
>>> > > if let x = x {
>>> > > foo.bar(x: x)
>>> > > }
>>> > > ```
>>> > >
>>> > > What do you think?
>>> > >
>>> > > Thanks,
>>> > > Justin
>>> > >
>>> > > _______________________________________________
>>> > > swift-evolution mailing list
>>> > > [email protected]
>>> > > <mailto:[email protected]>(mailto:[email protected]
>>> > > <mailto:[email protected]>)
>>> > > https://lists.swift.org/mailman/listinfo/swift-evolution
>>> > > <https://lists.swift.org/mailman/listinfo/swift-evolution>
>>> >
>>> >
>>> >
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