Hi All,

I want to print some object information for debugging. But the name of class is incorrect. I do not know why.


module test;

class A {
  char[] data;
  public char[] toString() {
    return "<" + this.classinfo.name + ": " + data + ">";
  }
}

class B: A {
  char[] data2;
  public override char[] toString() {
    return "<" + this.classinfo.name + ": " + super.toString + ", " + data2
+ ">";
  }
}

auto b = new B;
b.data = "hello";
b.data2 = "world";
Cout(b.toString); // <test.B: <test.B: hello>, world>


The expected result should be:
<test.B: <test.A: hello>, world>

But the actual result is:
<test.B: <test.B: hello>, world>

Hello Qian,

> Hi All,
> 
> I want to print some object information for debugging. But the name of
> class is incorrect. I do not know why.
> 
> module test;
> 
> class A {
> char[] data;
> public char[] toString() {
> return "<" + this.classinfo.name + ": " + data + ">";
> }
> }
> class B: A {
> char[] data2;
> public override char[] toString() {
> return "<" + this.classinfo.name + ": " + super.toString + ", " +
> data2
> + ">";
> }
> }
> auto b = new B;
> b.data = "hello";
> b.data2 = "world";
> Cout(b.toString); // <test.B: <test.B: hello>, world>
> The expected result should be:
> <test.B: <test.A: hello>, world>
> But the actual result is:
> <test.B: <test.B: hello>, world>

use typeof(this).classinfo.name to get type of A. "this" returns runtime type of instance, "typeof(this)" return static type.

http://www.digitalmars.com/d/1.0/expression.html

btw. I noticed that you are using "+" for string concatenation, how is possible that your program even comiples??? "~" should be used for string concatenation.

On Thu, 03 Dec 2009 11:01:29 +0100, Qian Xu <qian.xu@funkwerk-itk.com> wrote:

>Hi All,
>
>I want to print some object information for debugging. But the name of class is incorrect. I do not know why.
>
>
>module test;
>
>class A {
>  char[] data;
>  public char[] toString() {
>    return "<" + this.classinfo.name + ": " + data + ">";
>  }
>}
>
>class B: A {
>  char[] data2;
>  public override char[] toString() {
>    return "<" + this.classinfo.name + ": " + super.toString + ", " + data2
>+ ">";
>  }
>}
>
>auto b = new B;
>b.data = "hello";
>b.data2 = "world";
>Cout(b.toString); // <test.B: <test.B: hello>, world>
>
>
>The expected result should be:
><test.B: <test.A: hello>, world>
>
>But the actual result is:
><test.B: <test.B: hello>, world>
>
>

this.classinfo can be seen as a virtual function returning the
classinfo for the actual class instance and typeof(this).classinfo -
as a static function returning the classinfo of the compile-time type
of this (that is the class where it is called). So, your example
should be rewritten (D2):

import std.stdio;

class A {
  string data;
  public string toString() {
    return "<" ~ typeof(this).classinfo.name ~ ": " ~ data ~ ">";
  }
}

class B: A {
  string data2;
  public override string toString() {
    return "<" ~ typeof(this).classinfo.name ~ ": " ~ super.toString ~
", " ~ data2 ~ ">";
  }
}


void main()
{
    auto b = new B;
    b.data = "hello";
    b.data2 = "world";
    writeln(b.toString);
}

Michal Minich wrote:
> 
> btw. I noticed that you are using "+" for string concatenation, how is possible that your program even comiples??? "~" should be used for string concatenation.

sorry, it was my type error. the code is not real ^^)

Max Samukha wrote:

> 
> this.classinfo can be seen as a virtual function returning the
> classinfo for the actual class instance and typeof(this).classinfo -
> as a static function returning the classinfo of the compile-time type
> of this (that is the class where it is called). So, your example
> should be rewritten (D2):
> 

Thanks. You made my day