在Haxe中，如何读取宏内的变量名？

Question

I'm trying to use Macros to convert some variable declarations from this:

function test():Void {
    var someComp:Component = __SOME_MACRO__();

    // Or...
    @getCompById var someComp:Component;

    // Or even simpler...
    getCompById(someComp, Component); //do some fancy macro magic...
    // Also, if it's not possible/easy with a variable ...
    getCompById("someComp", Component); //with a string of the variable name.
}

... to this:

function test() {
    var someComp:Component = cast container.getCompById("someComp");
}

I'm leaning more toward the 3rd option (shorter syntax, same results).

But I have no idea how to write the macro (should it take a String as parameter? An expression?) and how to properly return that as a macro expression.

This is the (broken) code I've got so far:

macro static function getCompById(someVar:Expr, typeVar:Expr) {
    return macro {
        var someVar:typeVar = cast container.getCompById("someVar");
    };
}

Any ideas?

Answer 1

The issue with the code you posted is first that you'd need reification escaping mechanisms for this to work correctly - so the first change would be to use the macro escapes:

return macro var $someVar:$typeVar = cast container.getCompById($v{someVar});

Now there will be some problems with this: It's expecting someVar to be of type String, and typeVar to be of type ComplexType . It's easy to get the string component from an Expr . It's not so easy however to transform an Expr into ComplexType . The easiest way to do that is to use the tink_macros library and use asComplexType

So the (untested) code will look something like:

using tink.MacroAPI;
using haxe.macro.Tools;
macro static function getCompById(someVarExpr:Expr, typeVarExpr:Expr)
{
  var typeVar = typeVarExpr.toString().asComplexType();
  switch (someVarExpr.getIdent())
  {
    case Success(someVar):
      return macro var $someVar:$typeVar = cast container.getCompById($v{someVar});
    case Failure(error): throw error;
  }
}