Very cool!
func foo() -> Int { return 17 }
func bug1() -> Int {
return
foo() // Compiler says: Expression following ‘return'
// is treated as an argument of the 'return'.
}
var x = 0
func bug2() {
return x = 4 // not even a warning – should be an error
}
print(bug1()) // prints 17
bug2()
Dave
bug1() suggests that return be one of perhaps a set of special cases where line
wrap is illegal.
bug2() is a compiler bug IMO.
> On 2017-10-15, at 8:32 AM, Mike Kluev via swift-evolution
> <[email protected]> wrote:
>
> on Date: Fri, 13 Oct 2017 20:21:22 -0700 Chris Lattner <[email protected]
> <mailto:[email protected]>> wrote:
>
> We already have whitespace sensitive rules to handle this. There is no
> fundamental implementation difference that I see between separating the
> elements of lists (which are expressions) and the elements of statements
> (which can be expressions):
>
> func foo() -> Int { … }
>
> func statements() {
> foo()
> foo()
> }
>
> let list = [
> foo()
> foo()
> ]
>
> i was beaten by these optional semicolons...
>
> override func viewDidLoad() {
> super.viewDidLoad()
> return // put it ad-hoc to temporarily circumvent the rest of the code
>
> someView = SomeView(frame: view.bounds) // *
> view.addSubview(someView) // **
> ...
> }
>
> so i put that ad-hoc return statement to circumvent the rest of the code
> temporarily. of course i didn't put a semicolon after "return" as that skill
> was long lost. to my surprise the app crashed, and nowhere else but in the
> code that i thought was disabled...
>
> further investigation showed that in this case compiler was treating the
> statement after return which happened to have the matching type “Void” as
> part of return statement.
>
> should the function return type was, say, Int - that wouldn’t happen. or
> should the next statement was of a different type - that wouldn’t happen. in
> this case i was just “lucky”. here semantic information (matching vs non
> matching types) is clearly "aiding" syntax parsing and sometimes it leads to
> a surprising results.
>
> there was a warning on the * line:
> “warning: expression following 'return' is treated as an argument of the
> 'return’”
>
> and another warning on the ** line:
> “warning: code after 'return' will never be executed”
>
> as i was prepared to get the warning about the code being unused in the first
> place, i didn’t pay too much attention to the exact wording of that
> warning... and was beaten by it.
>
> Mike
>
> _______________________________________________
> swift-evolution mailing list
> [email protected]
> https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
[email protected]
https://lists.swift.org/mailman/listinfo/swift-evolution
