[swift-evolution] Extending declaration scope to condition for `repeat { } while ()`

[Sean Heber]

I’ve wanted this myself, too, so I’m generally +1, although I’ve also wondered if maybe this syntax should be changed somehow. I’ve not put a lot of thought into it, and this perhaps has come up before, but I sort of wonder.. would it make more sense to get rid of the trailing “while” entirely?

Here’s what I’m thinking:

This repeats forever - infinite loop:

repeat {}

And to get out of the infinite loop, you’d just use an if or guard the same way you might in any other loop in some cases:

repeat {
  let success = doSomething()
  guard success else { break }
}

We could potentially even warn if you use a repeat {} without there being a break inside the body somewhere.

This way, we eliminate a special syntactical form (repeat/while has always felt weird in every brace-based language I’ve used) and just piggyback on the existing break/continue/guard/if mechanisms that are already there and common. Then we also don’t need to have a special “weird” rule where the scope of variables change magically for repeat/while.

l8r
Sean



> On Jul 18, 2016, at 12:52 PM, Braeden Profile via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Good morning, Swift community!
> 
> I’ve come across a situation a number of times where I write code that has to try something one or more times using a `repeat…while` loop and the condition relies upon variables that should be declared within the scope of the loop.
> 
> repeat
> {
> 	let success = doSomething()
> }
> while !success
> 
> The compiler unnecessarily prohibits this:  “Use of unresolved identifier four.”  In this simple case, we can write:
> 
> repeat
> { }
> while !doSomething()
> 
> But in a more complex situation, we are forced to write:
> 
> var success: Bool
> repeat
> {
> 	success = doSomething()
> }
> while !success
> 
> 
> We could change this so that the declarations within the top level scope of the loop are accessible from the condition.
> 
> Thanks for reading my first post to the Swift discussion board!
> —Braeden
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