[swift-evolution] Making capturing semantics of local

[Mike Kluev]

on Wed, 25 Oct 2017 13:41:40 +0200 David Hart <david at hartbit.com> wrote:

class A {
>     func foo() {
>         func local() {
>             bar() // error: Call to method ‘bar' in function ‘local'
> requires explicit 'self.' to make capture semantics explicit
>         }
>
>         // ...
>     }
> }
>

it's not only about calling "bar"... any variable access will require self.
which will be quite annoying, especially given the fact that "local" my not
even be used in an escaping context discussed. (*)

i think it is more consistent to prepend local with self if it is used in
an escaping context:

func foo() {

    func local() {
        bar()              // no self needed here ever
        variable = 1   // no self needed here, ever
    }

    func otherLocal() {
        print("i am not capturing self")
    }

    DispatchQueue.main.async {
        local()            // error without self
        self.local()       // ok
        otherLocal()       // ok without self
    }
}

(*) interestingly, closures always treat themselves as "escaping", even if
it's not the case, e.g. even if i only use them in a non-escaping contexts.
worth to add an explicit attribute to denote non-escaping closures?

let closure = @nonescaping {
    print("i am not escaping")
    variable = 1 // ok without self
}

DispatchQueue.main.async(execute: closure) // error, non escaping closure
passed

Mike
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