1: Detection of an array type? 2: Constraints type of function parameter?

[Tom]

Hi!

1.: There is a method to detect a type of an array, if it is typed? Like var as:Array<String> = [];.

trace(Type.typeof(as));

Trace out: TClass(#Array), nothing more.

2.: I need a function, which has 2 parameters:

function test(obj:Dynamic, params:Dynamic) { }

The params variable can be constrained to String, or Array<String>?
The manual doesn't help me out. :-/

Thanks in advance!
Tom

[Simon Krajewski]

On 28 Aug 2014 10:49, "Tom" <hortoba...@gmail.com> wrote:
>
> Hi!
>
> 1.: There is a method to detect a type of an array, if it is typed? Like var as:Array<String> = [];.
> trace(Type.typeof(as));
>
> Trace out: TClass(#Array), nothing more.

There's no cross-target representation of runtime type parameters. This should be obvious if you're looking at targets like Javascript where you cannot tell what kind of elements `[]` has.

If your array has an element you can just typeof that.

> 2.: I need a function, which has 2 parameters:
>
> function test(obj:Dynamic, params:Dynamic) { }
>
> The params variable can be constrained to String, or Array<String>?
> The manual doesn't help me out. :-/

The real question is how you would use a thusly constrained type. The only thing they have in common is the length field, so you could use `{length:Int}` instead of Dynamic.

There are tricks using abstracts here, but this then requires runtime switching on something in order to figure out what kind of value you are dealing with.

Simon

[Tom]

I only want to allow these 2 types, that already the compiler throws error, if the type mismatch.
I can figure out in runtime, which params was passed, by the Std.is(params, String) code.

Tom

[Tom]

Nobody know any solution to detect an array type, and/or contraint a function second parameter to certain types?

[Simon Krajewski]

The whole idea is so horrible you might as well use Dynamic.

Simon

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[Gama11]

It is possible to use an abtract for this "either or" kinda thing, but the underyling type will still be Dynamic, so use with care, if at all.

class Test {

    static function main() {

        stringOrArrayString("Test");

        stringOrArrayString(["T", "e", "s", "t"]);

        

        // does not compile

        //stringOrArrayString(1);

    }

    

    static function stringOrArrayString(s:Either<String, Array<String>>) {

        if (Std.is(s, String)) {

            trace("String");

        } else {

            trace("String Array");

        }

    }

}

abstract Either<T1, T2>(Dynamic) from T1 from T2 to T1 to T2 {}

See on try.haxe.org.

[Tom]

Thanks, it maybe works.

Then only one more problem remains: can be detect type of an array, if it is strictly typed?