> On Aug 15, 2016, at 9:46 AM, Justin Jia via swift-evolution
> <swift-evolution@swift.org> 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.
> ```
>
> 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 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<swift-evolution@swift.org
> > <mailto:swift-evolution@swift.org>(mailto:swift-evolution@swift.org
> > <mailto:swift-evolution@swift.org>)>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
> > > swift-evolution@swift.org
> > > <mailto:swift-evolution@swift.org>(mailto:swift-evolution@swift.org
> > > <mailto:swift-evolution@swift.org>)
> > > https://lists.swift.org/mailman/listinfo/swift-evolution
> > > <https://lists.swift.org/mailman/listinfo/swift-evolution>
> >
> >
> >
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