Make dot shorthand work with generics and existentials

Evolution Pitches
29

I would like to see some kind of feature like this. In my own codebase, I have wanted protocol metatype properties with less complex cases, in the following approximate pattern:

protocol CustomDelegate { 
    func complexRequirementsHere()
}
class DefaultCustomDelegate : CustomDelegate {
}

func performAction(withDelegate delegate: CustomDelegate) {
    ....
}

performAction(withDelegate: .default) // versus currently performAction(withDelegate: DefaultCustomDelegate())

The way I imagined this feature being expressed is something like

extension CustomDelegate.Type {
    var `default`: DefaultCustomDelegate { return DefaultCustomDelegate() }
}

It feels like it falls out quite naturally, with the goal of better call-site readability. Admittedly, I haven't thought of all the possible applications of this, like more complex generic expressions, but I thought I'd contribute another motivating use case (and syntax suggestion) to the thread.

Last year, I identified where this could potentially be used to improve the RandomNumberGenerator API.

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