I think the `?` will make the return an optional. So your example should add
another ? at the end.
```
print(foo(bar(42)?, baz(42)?)?)
```
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)
}
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)>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)
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
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