[swift-evolution] [Idea] custom infix functions

[Vladimir.S]

I don't think we should rely only on XCode editor as Swift is open source 
now and is used on other systems like Linux where we have no XCode. And IMO 
language should not rely on any editor.
Just my opinion. Probably others will find this idea useful.

As for "with". Yes, I understand that this is just an example. I just 
wanted to point that "with" feature has some difficulties in implementation 
and this is why I propose to have it out-of-box in language or in standard lib.

Btw, your code does not work. Please check. I replaced to
let value = with(B()) {
    $0.x = 40
}
and had the similar error message(Error running code: ...)

On 22.04.2016 23:15, Adrian Zubarev via swift-evolution wrote:
> I know that this might be a bit confusing but at least for a syntax
> highlighting editor this shouldn’t be a problem. Any custom function is
> displayed with a different color (at least Xcode do).
>
> For structs one could use:
>
> struct B { var x = 10 }
>
> func with<T>(lhs: T, rhs: (inout T) -> Void) -> T {
>
>    var mutableValue = lhs
>    rhs(&mutableValue)
>    return mutableValue
> }
>
> let value = B() with {
>
>    $0.x = 40
> }
>
> This does even supports Swifty mutation if needed.
>
> `with` statement is just a single example we could create with infix functions.
>
>
> --
> Adrian Zubarev
>
> Am 22. April 2016 bei 22:05:11, Vladimir.S via swift-evolution
> (swift-evolution at swift.org <mailto:swift-evolution at swift.org>) schrieb:
>
>> On 22.04.2016 22:06, Adrian Zubarev via swift-evolution wrote:
>> > I’d like to throw an idea in the room and see where this will go.
>> >
>> > What if Swift would allow us to create custom infix functions?
>> > Does Swift need to ability of infix functions?
>> > How powerful can such a feature be?
>> > Pros and cons?
>> >
>> > There is a discussion about the `with` statement which we could develop
>> > with infix functions like so:
>>
>> IMO Such construction will looks like a language construction and will
>> confuse.
>>
>> And the function you suggest as replacement for "with" feature will *not*
>> correctly handle struct instances (Swift 3.0 mar 24):
>>
>> struct B { var x = 10 }
>>
>> func with<T: AnyObject>(lhs: T, rhs: @noescape (T) -> Void) { rhs(lhs) }
>>
>> var b2 = B()
>> with(b2) { print($0.x) }
>>
>> It will produce this error :
>> --------------
>> Error running code:
>> l-value expression does not have l-value access kind set
>> ...
>> -------------
>>
>> This is why I propose to introduce standard "with" feature(language feature
>> or built-in method(s)/free function(s)) in Swift out-of-box i.e. tested and
>> well-working solution in any situation. Not some hack/workaround that each
>> one will write for himself and that will not work in some situation.
>>
>> I can implement "with" method in some way for struct that will work like
>> this:
>>
>> struct B {
>> var x = 10
>>
>> mutating func withInPlace(user: @noescape (inout B)->Void) -> B {
>> var copy = self
>> user(&copy)
>> self = copy
>> return self
>> }
>>
>> func with(user: @noescape (inout B)->Void) -> B {
>> var copy = self
>> user(&copy)
>> return copy
>> }
>> }
>>
>> var b1 = B().with {
>> $0.x = 100
>> }
>>
>> print("created b1.x = ", b1.x)
>>
>> b1.withInPlace { $0.x = 1000 }
>>
>> let c1 = b1.with {
>> print("b1.x = ", $0.x)
>> $0.x = 2000
>> }
>>
>> print("b1.x = ", b1.x)
>> print("c1.x = ", c1.x)
>>
>> But again, this is custom solution, we need standard and tested way to do
>> this.
>>
>>
>> >
>> > infix func with<T: AnyObject>(lhs: T, rhs: @noescape (T) -> Void) {
>> >
>> > rhs(lhs)
>> > }
>> >
>> > class A {
>> >
>> > func foo() {}
>> > }
>> >
>> > let instance: A = A() with {
>> >
>> > $0.foo()
>> > }
>> >
>> > So what does the Swift community think about that idea?
>> >
>> > --
>> > Adrian Zubarev
>> >
>> >
>> > _______________________________________________
>> > swift-evolution mailing list
>> > swift-evolution at swift.org
>> > https://lists.swift.org/mailman/listinfo/swift-evolution
>> >
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>
>
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