Macro to generate "value classes" in Haxe

Example.hx

import precog.macro.ValueClass;

class ABC implements ValueClass {
    var a: Int;
    var b: Bool;
    var c: String;
}

/*
class ABC extends ValueClass {
    public var a(default, null): Int;
    public var b(default, null): Bool;
    public var c(default, null): String;

    public function new(a: Int, b: Bool, c: String) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
}
*/

ValueClass.hx

package;

import haxe.macro.Expr;
import haxe.macro.Context;

@:remove @:autoBuild(ValueClassImpl.build())
extern interface ValueClass {}

class ValueClassImpl {
#if macro
    public static function build() {
        var fields = Context.getBuildFields();
        var args = [];
        var states = [];
        for (f in fields) {
            switch (f.kind) {
            case FVar(t,_):
                args.push({name:f.name, type:t, opt:false, value:null});
                states.push(macro $p{["this", f.name]} = $i{f.name});
                f.access.push(APublic);
            default:
            }
        }
        fields.push({
            name: "new",
            access: [APublic],
            pos: Context.currentPos(),
            kind: FFun({
                args: args,
                expr: macro $b{states},
                params: [],
                ret: null
            })
        });
        return fields;
    }
#end
}