How to get child class Type and members from parent class?

[zoujiaqing via Digitalmars-d-learn]

import std.stdio;


class A
{
    this(T)(T t)
    {

    }

    void write()
    {
        T _this = cast(T) this;
        writeln(this.v);
    }
}

class B : A
{
    string v = "hello";
}

void main()
{
    auto b = new B;

    writeln(b.write()); // print hello
}