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

[Taras Zakharko via swift-evolution]

This is definitively something very useful but it also introduces a strong 
asymmetry into Swift statements. In all control-flow statements, the condition 
is part of the outer scope. Or, to be more precise, its part of an intermediate 
scope between the outer and the inner scope (as you can declare variables in 
the condition which are invisible to the outer scope but visible to the inner 
scope). Your suggestion essentially moves the condition of repeat {} while () 
to the inner scope. I think that the more complex semantics is not worth the 
change. 

Here is how I deal with it btw:

process: do {

   let success = …


   guard success else { continue process }
}

Again, goto FTW :p

T.


> On 18 Jul 2016, at 19:52, Braeden Profile via swift-evolution 
>  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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Re: [swift-evolution] Extending declaration scope to condition for `repeat { } while ()`

[Erica Sadun via swift-evolution]

A few quick points. Apologies for the brevity.

1. Please take a look at the stateful version of `sequence`
2. Additive, non-breaking proposals should be deferred until next month.

In regard to point 1, create a sequence that terminates on false. 
So you can hack something up like this (of course, hopefully a little more 
elegant)

extension Bool {
var optionalPresentation: Bool? { return self ? self : nil }
}

// a fake example of terminating check
func doSomething() -> Bool {
return arc4random_uniform(10) < 9 // 10% chance of ending
}

for nextItem in Swift.sequence(
state: doSomething().optionalPresentation,
next: { _ in return doSomething().optionalPresentation }) {

// use nextItem state here
// body of loop
}

Best,

-- E


> On Jul 18, 2016, at 11:52 AM, Braeden Profile via swift-evolution 
>  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
> ___
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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

[Braeden Profile via swift-evolution]

Great point; an infinite loop syntax would make a lot of sense.  It seems good 
for it to have its own syntax, considering you must have a `break` or `return` 
to escape it.  `while true { }` provides the same functionality, though it 
seems a bit less direct in its purpose than `repeat {  }` could.

> On Jul 18, 2016, at 4:16 PM, Haravikk  wrote:
> 
> 
>> On 18 Jul 2016, at 21:32, Sean Heber via swift-evolution 
>> > wrote:
>> 
>> 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
> 
> That's a very interesting alternative, especially with a warning when there's 
> no break (or return), and it would be clearer about the scope. Actually now I 
> think about it, the repeat/while is a little odd in Swift since the while 
> condition doesn't require parenthesis, which is great for a regular while or 
> if condition because the braces give it structure, but that's not quite the 
> case with the repeat/while.
> 
> I'm fine either way, but this should be explored as well; guard in particular 
> goes well this style of repeat syntax. More interestingly though is that this 
> would actually allow us to write while loops as:
> 
>   repeat {
>   guard someCondition() else { break }
>   doSomething()
>   }
> 
> while would essentially just become a shorthand.

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

[Haravikk via swift-evolution]

> On 18 Jul 2016, at 21:32, Sean Heber via swift-evolution 
>  wrote:
> 
> 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

That's a very interesting alternative, especially with a warning when there's 
no break (or return), and it would be clearer about the scope. Actually now I 
think about it, the repeat/while is a little odd in Swift since the while 
condition doesn't require parenthesis, which is great for a regular while or if 
condition because the braces give it structure, but that's not quite the case 
with the repeat/while.

I'm fine either way, but this should be explored as well; guard in particular 
goes well this style of repeat syntax. More interestingly though is that this 
would actually allow us to write while loops as:

repeat {
guard someCondition() else { break }
doSomething()
}

while would essentially just become a shorthand.___
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Re: [swift-evolution] Extending declaration scope to condition for `repeat { } while ()`

[Xiaodi Wu via swift-evolution]

Another +1 here.
On Mon, Jul 18, 2016 at 15:08 Garth Snyder via swift-evolution <
swift-evolution@swift.org> wrote:

> +1. Write it up.
>
> Garth
>
>
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Re: [swift-evolution] Extending declaration scope to condition for `repeat { } while ()`

[Garth Snyder via swift-evolution]

+1. Write it up.

Garth


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

[Haravikk via swift-evolution]

Strong +1 from me, I actually ran into a bunch of cases like this recently, 
having to put a tracking variable outside the loop feels weird; it makes sense 
for a regular while loop, but I see no reason that repeat/while couldn't have 
values from the loop be in scope for its condition.

There is a very slim chance of breakage if a variable is shadowed, can we use 
that as an excuse to get this done in Swift 3? =D

> On 18 Jul 2016, at 18:52, Braeden Profile via swift-evolution 
>  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
> ___
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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

[Kevin Nattinger via swift-evolution]

I would love this behavior, I ran into a case just a week or two ago where I 
was wishing for this behavior.

That said, I’m not sure whether it would be possible / feasible for the 
compiler. And it’s additive so it will have to wait for after Swift 3 is 
released.

> On Jul 18, 2016, at 10:52 AM, Braeden Profile via swift-evolution 
>  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
> ___
> swift-evolution mailing list
> swift-evolution@swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution

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

[Braeden Profile via swift-evolution]

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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