Open Radar

 
Summary:
An autoclosure parameter whose type throws requires that client code try when passing the de-braced closure:

consume_an_error_from_a_throwing_func(try a_func_that_throws)

However, in the context of a closure, this syntax does not work properly.  In particular, the error "leaks" out of <<try a_func_that_throws>> into the surrounding scope, making the closure be inferred to be of throwing type.

let c = {
    consume_an_error_from_a_throwing_func(try a_func_that_throws)
}

Here, c is inferred to be of type () throws -> ().  However, consume_an_error_from_a_throwing_func, the only function called from this closure, does not throw.  (a_func_that_throws is called inside the implementation of consume_an_error_from_a_throwing_func and consequently any error it throws must be handled there.)  The inferred type of c should be () -> (), a non-throwing function.

Steps to Reproduce:
Attempt to compile the following code with Xcode7 Beta 5.

func attempt<T>(@autoclosure f: () throws -> T) -> T? {
    //...
}

func create_int() throws -> Int {
    return 1
}

func call(function: () -> ()) {
    function()
}

call {
    attempt(try create_int())
}

func direct() {
    attempt(try create_int())
}

Notice the compile error on the line where call is invoked: Invalid conversion from throwing function of type '() throws -> _' to non-throwing function of type '() -> ()'.

Expected Results:
This code should compile just fine.

Actual Results:
A compile error is raised.

Version:
Xcode 7 Beta 5

Notes:


Configuration:
MacBook Pro Retina

Attachments: