[swift-evolution] [Pitch] Make `default` function parameter values more transparent

Charlie Monroe charlie at charliemonroe.net
Sun Jun 12 23:27:22 CDT 2016

> On Jun 11, 2016, at 3:35 PM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
> I just installed the current Swift 3 snapshot to play around with it (last from may crashed my Xcode all the time).
> I wanted to re-build a small project with (currently implemented) Swift 3 changes. Basically I had to look up on GitHub what the default value for deinitialize(count:) function was for UnsafeMutablePointer, just because Xcode and the docs can’t tell me that:
> /// De-initialize the `count` `Pointee`s starting at `self`, returning
> /// their memory to an uninitialized state.
> ///
> /// - Precondition: The `Pointee`s at `self..<self + count` are
> ///   initialized.
> ///
> /// - Postcondition: The memory is uninitialized.
> public func deinitialize(count: Int = default)
> To cut it short:
> Could we make default function parameter values more transparent in Swift 3?
> Why are default parameter values translated to default rather than the actual value?
I guess that in some cases you don't want the default value to be known, or is irrelevant. Most importantly, it can be a more complex expression - e.g. creating an object and calling something on it:

private let mySecretNumber = 0x999
public func deinitialize(count: Int = NSProcessInfo().processorCount + mySecretNumber)

And that's a pretty example, it can get much nastier. Since mySecretNumber is private, it definitely cannot be exposed.

> Can we make this independent from docs?
> -- 
> Adrian Zubarev
> Sent with Airmail
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