[swift-users] Optional binding with non-optional expression

[Zhao Xin]

Then I knew it.

if let a: A = A() { // this is a warning as it treats like always true

    print("something") // this line always runs

}

For

if let a = A() { // show an error as the compiler thinks you are missing
something.

}

For me, the first example, explicitly given the type of `a`, so it is a
warning. The second example, is one step farther than the first one. And it
is shown as an error.

Each one of them is correct by itself. But putting together, there is a
self-contradictory feeling.


Zhao Xin


On Sun, Jun 4, 2017 at 6:00 PM, Martin R <martinr448 at gmail.com> wrote:

> I don’t think that explains it (or perhaps I did not understand your
> response correctly).
>
> Here is the same issue with a custom type (which does not have a failable
> initializer):
>
>    struct A { }
>
>    if let a = A() { }
>    // error: initializer for conditional binding must have Optional type,
> not 'A'
>
>    if let a: A = A() { }
>    // warning: non-optional expression of type 'A' used in a check for
> optionals
>
>
> > Am 02.06.2017 um 15:49 schrieb Zhao Xin <owenzx at gmail.com>:
> >
> > I think it did an unnecessary implicitly casting. For example,
> >
> > let y = Int(exactly: 5)
> > print(type(of:y)) // Optional<Int>
> >
> > You code equals to
> >
> > if let y:Int = Int(exactly: 5) { }
> >
> > However, I don't know why it did that. Maybe because of type inferring?
> >
> > Zhaoxin
> >
> > On Fri, Jun 2, 2017 at 8:40 PM, Martin R via swift-users <
> swift-users at swift.org> wrote:
> > This following code fails to compile (which is correct, as far as I can
> judge that):
> >
> >    if let x = 5 { }
> >    // error: initializer for conditional binding must have Optional
> type, not 'Int'
> >
> > But why is does it compile (with a warning) if an explicit type
> annotation is added?
> >
> >    if let y: Int = 5 { }
> >    // warning: non-optional expression of type 'Int' used in a check for
> optionals
> >
> > Tested with Xcode 8.3.2 and both the build-in Swift 3.1 toolchain and
> the Swift 4.0 snapshot from May 25, 2017.
> >
> > I am just curious and would like to understand if there is fundamental
> difference between those statements.
> >
> > Regards, Martin
> >
> >
> >
> > _______________________________________________
> > swift-users mailing list
> > swift-users at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-users
> >
> >
>
>
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