[swift-evolution] [Review] SE-0007 Remove C-style for-loops with conditions and incrementers

[Stephen Celis]

On Thu, Dec 10, 2015 at 12:16 PM, Michel Fortin via swift-evolution <
swift-evolution at swift.org> wrote:

> You can't replace C-style for loops with for-in in the general case. Using
> a "while" loop will always be possible, but also much more verbose. For
> instance, take this loop iterating downward over i and j in lockstep:
>
>         for var i = 10, j = 20; i > 0 && j > 0; i -= 1, j -= 2 {
>                 ... loop body ...
>         }
>
> The only fully-compatible while loop that makes sense is this one:
>
>         do {
>                 var i = 10
>                 var j = 20
>                 var first = true
>                 while true {
>                         if first { first = false }
>                         else { i -= 1; j -= 2 }
>                         guard i > 0 && j > 0 else { break }
>                         ... loop body ...
>                 }
>         }
>
> If the loop body contains a continue, it works. If the loop body mutates
> one of the loop variables, it works. If the loop throws, it works. If the
> outer scope has a variable with the same name, it works! There is no code
> duplication. But oh boy, the boilerplate!
>

Can't you do the following?

    var i = 10, j = 20; while i > 0 && j > 0 { defer { i -= 1; j -= 2 }
        // ...
    }

I adjusted the formatting to more closely match the C-style for loop, so if
you were to use a more Swift-y style, it would be slightly more verbose.

Stephen
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