Creating map using templated type T as key type

[Jason Hobbs]

Hey guys,

I'm updating some codes from Haxe 2.10 to Haxe 3 and I'm struggling a bit here with the new Maps and/or generic stuff!

Say I have a generic class which contains the member maps as follows.

class DAG<T>

{

var m:Map<T, String >;

var m1:Map<String, T>;

public function new()

{

                // error: Abstract Map has no @:to function that accepts IMap<utility.DAG.T, Array<utility.DAG.T>>

m = new Map<T, String>();

// compiles fine

m1 = new Map<String, T>();

}

}

This will compile error with the error in the comment if T is used as the key type however it works fine as the value Type.

Any suggestions how I can pass a type into DAG to be the key type of the map?

Thanks

J

[Jason Hobbs]

Just to add that i have 

@:generic class DAG<T>

[Joshua Granick]

I only got this to work by hard-coding IntMap or StringMap rather than the Map abstract :(

[TopHattedCoder]

I think it's because the abstract functions for conversion between a Map and ObjectMap use a {} for the key instead of Dynamic, try constraining the parameter to {}, like so:

class DAG<T:{}> {
  var m:Map<T, String >;
  var m1:Map<String, T>;
  public function new() {

[Jason Hobbs]

Awesome thanks man, That works like a charm!

[Joshua Granick]

What exactly does this syntax mean?

[Stephane Le Dorze]

Works indeed but one needs to understand that it will not select the most specific implementation - for instance if T is a String.

[Simon Krajewski]

Am 27.06.2013 09:31, schrieb Stephane Le Dorze:
> Works indeed but one needs to understand that it will not select the
> most specific implementation - for instance if T is a String.

Considering @:generic, the real problem is that the compiler tries to
post-process the unapplied version of the class and then encounters the
error. This would be this issue:
https://github.com/HaxeFoundation/haxe/issues/1578

The concrete classes should actually use StringMap/EnumValueMap if the
type parameter matches. This should be tested though.

Simon

[Jason Hobbs]

So if T is a string in this example it will still use ObjectMap as opposed to StringMap?

[Nicolas Cannasse]

Le 27/06/2013 07:43, Joshua Granick a �crit :

> What exactly does this syntax mean?

>>> class DAG<T:{}> {

It means that "T" should be at least the empty structure {}, so any kind
of object will work.

Best,
Nicolas

[Joshua Granick]

So it prevents it from being null or Void?


On Fri, 28 Jun 2013 13:24:34 -0700, Nicolas Cannasse <ncan...@gmail.com> wrote: