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

[Matheus via Digitalmars-d-learn]

On Wednesday, 20 November 2019 at 13:46:07 UTC, Jacob Carlborg 
wrote:
On Wednesday, 20 November 2019 at 10:05:11 UTC, zoujiaqing 
wrote:
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
}

You can use a template this parameter [1], like this:

import std.stdio;

class A
{
    void write(this T)()
    {
        T self = cast(T) this;
        writeln(self.v);
    }
}

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

void main()
{
    auto b = new B;
    b.write();
}

[1] https://dlang.org/spec/template.html#template_this_parameter

--
/Jacob Carlborg

I'm not the OP but a lurker, and this is new to me, I mean in 
your example you're accessing a member "v" which wasn't defined 
in the Parent class.

So if someone creates something like this:

class C : A{
    string x = "world";  // x instead of v
}

Not the "x" instead of "v", of course it will only get an 
compiler error if that function is called in by "C" object.

I think this is a powerful and weird feature at the same time, 
because some could write a code like this:

import std.stdio;

class A{
    void write(this T)(){
        T self = cast(T) this;
        writeln(self.v);
    }

    void write2(this T)(){
        T self = cast(T) this;
        writeln(self.x);
    }
}

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

class C : A{
    string x = "world";
}

void main(){
    auto b = new B;
    b.write();

    auto c = new C;
    c.write2();
}

This is a different way of designing things, do people use this 
often?

Matheus.