I think a better way of achieving this would be to use the already existing
`where` keyword in loops. The way it works right now is as follows:
let many = [1, 2, 3, 4, 5]
for each in many where each % 2 == 0 {
print("found an even number: \(each)")
}
Unfortunately, unlike all other conditional scopes, `where` does not allow
`let` and `var` bindings in it, so I'd suggest we add ability to do that:
let many: [Int?] = [1, 2, nil, 3, 4, nil, 5]
for each in many where let number = each {
print("found a non-nil number: \(number)")
}
Or, more interestingly:
for each in many where let number = each, number % 2 == 0 {
print("found a non-nil even number: \(number)")
}
And in case of a while loop:
var optional: Int? = 1
while let nonoptional = optional {
if nonoptional >= 10 {
optional = nil
}
optional = nonoptional + 1
}
But this is only for optional unpacking, so another addition would be to allow
any `let` and `var` bindings in conditional scopes without them contributing to
the condition itself:
while let a = 0, a < 10 {
a += 1
print(a)
}
And finally, allow these bindings in `repeat`:
repeat let a = 0 {
a += 1
print(0)
} while a < 10
I think **if** the core team would consider this a worthwhile addition, this
would be a less invasive and more intuitive way of achieving what you want.
> On Jun 10, 2017, at 1:31 PM, Haravikk via swift-evolution
> <[email protected]> wrote:
>
> Not sure if my e-mail didn't go through or if discussion just fizzled out;
> one other benefit if we ever move to a proper message board is we might gain
> the ability to bump topics. Anyway, I'll resend my message just in case:
>
>
>
> Just to add my thoughts, as I like the idea of adding the variables to the
> start somehow, but was wondering if might make sense to have a keyword such
> as "using", but allow it on all block statements, like-so:
>
> // Original use-case of repeat … while
> repeat using (var i = 0) {
> // Do something
> } while (i < 20)
>
> // for … in demonstrating combination of using and where
> for eachItem in theItems using (var i = 0) where (i < 20) {
> // Do something either until theItems run out or i reaches 20
> }
>
> // Standard while loop
> while let eachItem = it.next() using (var i = 0) where (i < 20) {
> // As above, but with an iterator and a while loop and
> conditional binding to also stop on nil
> }
>
> // Closure with its own captured variable
> let myClosure:(Int) -> Int = using (var i = 0) { i += 1; return i * $0 }
>
> // If statements as well
> if somethingIsTrue() using (var i = 0) where (i < 20) {
> // Do something
> }
>
> // Or even a do block; while it does nothing functionally new, I quite
> like it aesthetically
> do using (var i = 0) {
> // Do something
> }
>
> Unifying principle here is that anything created in the using clause belongs
> to the loop, conditional branch etc. only, but exists outside the block
> itself (thus persisting in the case of loops and closures). I quite like the
> possible interaction with where clauses here as a means to avoid simple inner
> conditionals as well.
>
> Basically the two clauses can work nicely together to avoid some common inner
> and outer boilerplate, as well as reducing pollution from throwaway variables.
>
> Only one I'm a bit iffy on is the closure; I'm trying to avoid declaring the
> captured variable externally, but I'm not convinced that having using on its
> own is clear enough?
>
> Anyway, just an idea!
>
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