[swift-evolution] [Pitch] Extending [at]autoclosure

[Adrian Zubarev]

Hello folks,

Here is a quick and straightforward pitch about @autoclosure. Currently the attribute indicates that the caller has to pass an expression so that the braces can be omitted. This is a convenient behavior only, but it also has it’s shortcomings.

I would like to propose an extension of that behavior.


1. Allow access to arguments and shorthand argument names:
// Bug: https://bugs.swift.org/browse/SR-5296
func foo(_ test: @autoclosure (Int) -> Int = { $0 }) {
    print(test(42))
}

// Convenient access using shorthand arguments
foo(Int(Double($0) * 3.14)))

2. Make @autoclosure only wrap when necessary:
func bar(_ test: @autoclosure () -> Int) {
    print(test())
}

let test = { 42 }

// function produces expected type 'Int'; did you mean to call it with '()'?
bar(test)

3. Extend @autoclosure to closure types in general (this change is for consistent alignment):
// Note how we're using the shorthand argument list for this expression
let uppercaseWrapper: @autoclosure (String) -> String = $0.uppercased()


-- 
Adrian Zubarev
Sent with Airmail
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