CODEWITHSUNDEEP
macroshaxe
TheSHEEEP
TheSHEEEP

Reputation: 3132

Creating a function in a macro

I am trying to add a static variable and a static function to all instances of a class and its child classes using the @:build and @:autoBuild macros.

I managed to get the static variable working, but I have no idea how to "build" the function from the various EFunction, EFor, etc.

Here is the code I have so far:

macro static public function addGetId() :Array<Field>
{
    var fields : Array<Field> = Context.getBuildFields();

    // The static _id field
    var idField = {
        name : "_id",
        doc : null,
        meta : [],
        access : [AStatic, APrivate],
        kind : FVar(macro : Int, macro -1),
        pos : Context.currentPos()
    };

    // The getId function field
    var getIdField = {
        name : "getId",
        doc : "Returns the ID of this command type.",
        meta : [],
        access : [AStatic, APublic],
        kind : FFun({
            params : [],
            args : [],
            expr: // What do I have to write here???
            ret : macro : Int
        }),
        pos : Context.currentPos()
    };

    fields.push(idField);
    fields.push(getIdField);
    return fields;
}

Here is how the function that I want to add would look like in normal code, if it was actually in the .hx file:

public static function getId() : Int
{
    if (_id == -1)
    {
        _id = MySingleton.getInst().myGreatFunction()
    }
    return _id;
};

So it references the newly added _id variable as well as some singleton class function.
So: How would the complete getIdField() look like?

Bonus Question:
My biggest problem with this is the complete lack of documentation on these features as well as any useful examples in the manual. Is there any actually useful tutorial for creating functions like this?

Bonus Bonus Question:
What is the difference between params and args in FFun?

Upvotes: 5

Views: 1051

Answers (1)

Gama11
Gama11

Reputation: 34148

You can make use of reification to write the body of the function like you would in regular Haxe code:

expr: macro {
    if (_id == -1) {
        _id = 0;
    }
    return _id;
},

params is a list of type parameters, args is the list of arguments the function receives. There's a trivia section about this on the Haxe Manual:

Trivia: Argument vs. Parameter

In some other programming languages, argument and parameter are used interchangeably. In Haxe, argument is used when referring to methods and parameter refers to Type Parameters.

Upvotes: 5

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