哪些框架/语言支持运行时类创建？

function Foo(x, y, z)
{
        this.X = x;
        this.Y = y;
        this.Z = z;  var g = function()

}

var obj = new Foo(a,b,c);

function MakeFoo(x, y, z, f) //where parameter f is a function
{
    var g = function()
    {

        this.X = x;
        this.Y = y;
        this.Z = z;
        this.DoSomething = f;
    }

    return g;

}

var my_class = MakeFoo(a, b, c, function() { /* Do Stuff */ });
var obj = new my_class();

obj.DoSomething();