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;
}

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

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

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

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

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.