Duplicate parameter names

[markknol]

Is this expected behavior?

function func(a, a) trace(a);
func("Hello", "World");
// outputs "World"

(http://try.haxe.org/#bdE78)

In other languages you get an error like this: The parameter name 'a' is a duplicate.

[Simn]

That should surely be an error. I hope this is not a regression...

[back2dos]

I think that has always been the case. Given that you can write var a = "Hello", a = "World"; I would say it is only consistent.

On Fri, Jul 3, 2015 at 1:56 PM, Simon Krajewski notifications@github.com
wrote:

That should surely be an error. I hope this is not a regression...

—
Reply to this email directly or view it on GitHub
#4381 (comment)
.

[Simn]

It would be cool if the second a could reference the first one though. :P

[markknol]

I think especially in case of parameters you just want an error.

[back2dos]

@markknol I would speculate that it's meant to allow for function (_, _, theArgumentYouReallyWant) {}

@Simn It seems it can: http://try.haxe.org/#b94fE

Slightly off-topic: why was referencing previous variables in the same declaration allowed? I would say var x = y, y = x; is a very clear way to swap variables. And IIRC this was still possible a couple of years ago.

I see this:

{
   var a = exprA, b = exprB;
   somethingHere;
}

As this:

(function (a, b) {
   somethingHere;
})(exprA, exprB)

So I've always been puzzled by the fact that exprB may reference a. It feels uncomfortably close to JavaScript's weird scoping rules.

[markknol]

@back2dos Just curious; In which case would you define a function with those underscores?

[Simn]

I find it natural in a left-to-right kind of way. It's also trivial to generate it to our targets, whereas some swapping behavior would be tricky to get right.

[back2dos]

@markknol Consider a map with the standard JavaScript signature. In that case you would write [1, 2, 3].map(function (x, _, _) return x + 2).

[back2dos]

@Simn No doubt it is tricky, but you already got it right, given that this works already:

{
  var x = 5, y = 6;
  {
    var x = y;
  }
  {
    var y = x;
  }
}

Anyway, it's nothing we can change any time soon. This thread just reminded me of how odd I find it to be, so I had to ask ^^

[ncannasse]

We could forbid same-function-parameter-name, with the exception of underscore, that sounds like a good middle ground

[Simn]

Thinking about this now I don't think it's worth disallowing this. Who knows what crazy macro-generated functions might have duplicate argument names somewhere. I also don't think this would catch any programming errors.