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digitalmars.D.learn - override toString

reply Qian Xu <qian.xu funkwerk-itk.com> writes:
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>
Dec 03 2009
next sibling parent reply Michal Minich <michal.minich gmail.com> writes:
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.
Dec 03 2009
parent Qian Xu <qian.xu funkwerk-itk.com> writes:
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 ^^)
Dec 03 2009
prev sibling parent reply Max Samukha <spambox d-coding.com> writes:
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);
}
Dec 03 2009
parent Qian Xu <qian.xu funkwerk-itk.com> writes:
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
Dec 03 2009