Accessing Metadata on other classes within a Macro

[theRemix]

I don't know much about how to use macros, and i'm using haxe 2.10 at the moment

I'm going off of this guide http://haxe.org/manual/metadata

haxe.rtti.Meta won't work here

and i'm not sure how to actually access field metadata from Types in a macro context

import haxe.macro.Expr;

class MyClass {

  @:mydata(123) var myvar:String;

  

}

class MacroMeta {

  @:macro public static function getMeta() : Expr {

    var m = haxe.rtti.Meta.getFields(MyClass);

    trace(m);

    return { expr : EConst(CString("")), pos : haxe.macro.Context.currentPos() };

  }

  public static function main():Void{

    getMeta();

  }

  

}

the trace output:

MacroMeta.hx:11: {}

what is the correct way to access the metadata on the fields of another class?

[Juraj Kirchheim]

Use Context.resolve("full.path.ClassName") to get the Type, which with
a bit of luck is TInst. Then get the ClassType from that, then iterate
through the fields to find the one you're looking for, and then access
the metadata.

Regards,
Juraj

[theRemix]

Thanks for your guidance, however i don't understand how to do what you say.

Use Context.resolve("full.path.ClassName") to get the Type

there is no Context.resolve, do you mean Context.resolvePath( file : String ) : String ? or Context.getType( name : String ) : Type ?

Then get the ClassType from that

How do i get the ClassType? i'm not familiar with macros

this is what i have, and this doesn't work

@:macro public static function getMeta() : Expr {

    var t = haxe.macro.Context.getType("MyClass");

    // trace(t); // TInst(MyClass,[])

    var cl = Type.getClass(t);

    trace(cl); // null

    return { expr : EConst(CString("")), pos : haxe.macro.Context.currentPos() };

  }

[Juraj Kirchheim]

Yes, sorry. I meant Context.getType.

You would use a switch to get to the class:

switch haxe.macro.Context.getType("MyClass") {
case TInst(ref, _):
var cl:ClassType = ref.get();
case default:
}

Regards,
Juraj

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[Confidant]

I am also trying to access metadata from within a macro without much luck. My simplified code:

@:build(
    MacroClass.theMethod("cms/application/cms.php")
)
class GeneratedExtern implements Dynamic { }

class Main
{
@libdirLive("/path/to/lib") var ld1:String;

}

//in a separate file:
class MacroClass{
 macro static public function theMethod(filePath:String){
  switch Context.getType("Main") {
     case TInst(ref, params):

         var cl:ClassType = ref.get();

         trace(Meta.getFields(cl));
     default:
  }

 }
}

outputs:
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}
src/MacroClass.hx:85: {}

What should I do?

[Juraj Kirchheim]

Ok, here is the basic issue: you are trying to get the metadata through `haxe.rtti.Meta`. Unfortunately, the "r" in "rtti" stands for "runtime", so it is the wrong tool for the job. However, the solution is actually even simpler:

  trace(cl.meta.get());//traces the metadata of the class

  for (field in cl.fields.get())

    trace(field.meta.get());//traces the metadata of each field

I hope that clarifies things.

Best,

Juraj

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[Confidant]

Always ask the experts. :) Thanks—it works of course!