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digitalmars.D.learn - Pointers to methods

reply "nazriel" <spam dzfl.pl> writes:
Greetings.

While playing with D code (http://dpaste.dzfl.pl/c6d9e5bd) I 
noticed that I have no idea how to write equivalent to this C++ 
code:

http://dpaste.dzfl.pl/ae182695 *[1]

Could somebody point me out how to achieve same thing? Maybe I am 
missing something obvious? Thanks!

*[1] - code for lazy people :
#include <cstdio>

class A
{
	int x;

public:
	A(int y) : x(y){}

	void foo()
	{
		printf("::foo(), x: %d\n", x);
	}
};

class B : public A
{
public:
	B(int y) : A(y)
	{}		
};

int main(void)
{
	void (A::*fp)() = &A::foo;

	A a(3);
	B b(4);

	(a.*fp)();
	(b.*fp)();

	return 0;
}
Mar 03 2013
next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
nazriel:


 While playing with D code (http://dpaste.dzfl.pl/c6d9e5bd) I 
 noticed that I have no idea how to write equivalent to this C++ 
 code:


I think the answer to this so common question should go here 
(unless already present):
http://dlang.org/faq.html

Bye,
bearophile
Mar 03 2013
next sibling parent "nazriel" <spam dzfl.pl> writes:
On Monday, 4 March 2013 at 03:28:30 UTC, bearophile wrote:

 nazriel:


 While playing with D code (http://dpaste.dzfl.pl/c6d9e5bd) I 
 noticed that I have no idea how to write equivalent to this 
 C++ code:


 I think the answer to this so common question should go here 
 (unless already present):
 http://dlang.org/faq.html


If that question was asked before then I am very sorry.
Documentation doesn't mention this particular case.
All it mentions are delegates:

A a = new A();
auto fp = &a.func; // <- Not what I am asking about.

Also if you know the answer please, feel free to tell me.
It would speed up work with stuff I have to do hehe


 Bye,
 bearophile
Mar 03 2013
prev sibling parent "nazriel" <spam dzfl.pl> writes:
On Monday, 4 March 2013 at 03:28:30 UTC, bearophile wrote:

 nazriel:


 While playing with D code (http://dpaste.dzfl.pl/c6d9e5bd) I 
 noticed that I have no idea how to write equivalent to this 
 C++ code:


 I think the answer to this so common question should go here 
 (unless already present):
 http://dlang.org/faq.html


Oh, I also tried all variations of

(obj.*fpp)()
(obj).*fpp()
(obj).(*fpp)()
obj.*fpp()

Of course everything fails, either with parsing errors or 
resolution errors


 Bye,
 bearophile
Mar 03 2013
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/03/2013 07:21 PM, nazriel wrote:


 *[1] - code for lazy people :


Thank you very much for doing that. It is the only way to ensure that 
these threads will remain complete.

Here are two ways depending on what you need:

import std.stdio;

class A
{
     int x;

public:
     this (int y) { x = y; }

     void foo()
     {
         writefln("::foo(), x: %s", x);
     }
};

class B : A
{
public:
     this(int y)
     { super(y); }
};

void main()
{
     {
         auto a = new A(3);
         auto b = new B(4);

         // When objects are available up front, initialize the function
         // pointer by an object:
         auto fp = &a.foo;
         fp();
         fp = &b.foo;
         fp();
     }

     {
         // When no object is available up front, use a function literal 
to be
         // called with objects later on:
         auto fp = ((A o) => o.foo());

         auto a = new A(5);
         auto b = new B(6);

         fp(a);
         fp(b);
     }
}

Ali
Mar 03 2013
parent "nazriel" <spam dzfl.pl> writes:
On Monday, 4 March 2013 at 03:44:20 UTC, Ali Çehreli wrote:

 On 03/03/2013 07:21 PM, nazriel wrote:


 *[1] - code for lazy people :


 Thank you very much for doing that. It is the only way to 
 ensure that these threads will remain complete.

 Here are two ways depending on what you need:

 import std.stdio;

 class A
 {
     int x;

 public:
     this (int y) { x = y; }

     void foo()
     {
         writefln("::foo(), x: %s", x);
     }
 };

 class B : A
 {
 public:
     this(int y)
     { super(y); }
 };

 void main()
 {
     {
         auto a = new A(3);
         auto b = new B(4);

         // When objects are available up front, initialize the 
 function
         // pointer by an object:
         auto fp = &a.foo;
         fp();
         fp = &b.foo;
         fp();
     }

     {
         // When no object is available up front, use a function 
 literal to be
         // called with objects later on:
         auto fp = ((A o) => o.foo());

         auto a = new A(5);
         auto b = new B(6);

         fp(a);
         fp(b);
     }
 }


The 2nd one is what I was looking for.
Thanks a lot Ali.
Mar 03 2013