Scala like placeholder for types

[gregtitus]

@Jon_Hull

This would also apply to most names. For example, if I don't want to stop and think about what to call a function until after I have written it:

func ??? () -> Int {
    //I'll name it in a minute. Right now I want to work out the function itself...
}

This works today with editor placeholders. If you type:

func <#name#>() -> Int {
}

Then this won't cause any errors while you are still in the middle of writing, and only error if you explicitly try to compile. Not only that, but in a playground, instead of an error, having a placeholder is only a warning, so you can run the playground with this still in it. And, of course, Xcode treats it specially for you as a token that's easy to click on and replace.