[swift-evolution] [Idea] custom infix functions

[Adrian Zubarev]

Ooops, my bad, I didn’t scroll your reply to the very end and so I didn’t read your full answer.

The custom `with` statement with infix function was just an example that it might be possible to build.

It won’t look that 'hacky‘ if Swift would have an explicit protocol for all value types. Something like `AnyValueType`

Then we could easily overload such a custom infix function

infix func with<T: AnyValueType>(lhs: T, rhs: (inout T) -> Void) -> T {
		
	var mutableValue = lhs
	rhs(&mutableValue)
	return mutableValue
}

infix func with<T: AnyObject>(lhs: T, rhs: (T) -> Void) -> T {
		
	rhs(lhs)
	return lhs
}

There is also no chance of such usage, because the `with` function is marked as `infix`

struct B { var x = 10 }

let b = B()

with(b) { print($0.x) } // this won’t be possible at all, infix operators doesn’t allow that so why should infix functions?

As expected we will be able to do something like this:

let newImutableB = B() with {

   $0.x = 40 // mutation here is allowed, because we copy internally and path the new value back
}

Infix functions should forbid reserved functions names like `if`, `do`, `else` etc.


-- 
Adrian Zubarev

Am 22. April 2016 bei 22:15:26, Adrian Zubarev (adrian.zubarev at devandartist.com) schrieb:

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) 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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