What is the meaning of the value returned by the address operator applied to an instance member function as if that function were static?

class Foo
{
	void bar()
	{
	}
}

void main()
{
	writefln(&Foo.bar);
}

"Max Samukha" <samukha@voliacable.com> wrote in message news:11js039sich4vjo364at18so5m625bdvc8@4ax.com...
> What is the meaning of the value returned by the address operator applied to an instance member function as if that function were static?
>
> class Foo
> {
> void bar()
> {
> }
> }
>
> void main()
> {
> writefln(&Foo.bar);
> }

It's a function pointer to that method.  It's actually useful -- you can simulate pointer-to-members using this and delegates:

class A
{
    int mX;

    this(int x)
    {
        mX = x;
    }

    void foo(int y)
    {
        writefln(mX, ", ", y);
    }
}

void main()
{
    scope a = new A(5);
    a.foo(4);

    void delegate(int) dg;
    dg.funcptr = &A.foo; // <<- dah
    dg.ptr = cast(void*)a;
    dg(8);
}

On Sat, 31 Mar 2007 11:43:47 -0400, "Jarrett Billingsley" <kb3ctd2@yahoo.com> wrote:

>"Max Samukha" <samukha@voliacable.com> wrote in message news:11js039sich4vjo364at18so5m625bdvc8@4ax.com...
>> What is the meaning of the value returned by the address operator applied to an instance member function as if that function were static?
>>
>> class Foo
>> {
>> void bar()
>> {
>> }
>> }
>>
>> void main()
>> {
>> writefln(&Foo.bar);
>> }
>
>It's a function pointer to that method.  It's actually useful -- you can simulate pointer-to-members using this and delegates:
>
>class A
>{
>    int mX;
>
>    this(int x)
>    {
>        mX = x;
>    }
>
>    void foo(int y)
>    {
>        writefln(mX, ", ", y);
>    }
>}
>
>void main()
>{
>    scope a = new A(5);
>    a.foo(4);
>
>    void delegate(int) dg;
>    dg.funcptr = &A.foo; // <<- dah
>    dg.ptr = cast(void*)a;
>    dg(8);
>}
>
>
Thanks a lot. That's exactly what I need

Jarrett Billingsley wrote:
 > It's a function pointer to that method.  It's actually useful -- you can
> simulate pointer-to-members using this and delegates:
> 
> class A
> {
>     int mX;
> 
>     this(int x)
>     {
>         mX = x;
>     }
> 
>     void foo(int y)
>     {
>         writefln(mX, ", ", y);
>     }
> }
> 
> void main()
> {
>     scope a = new A(5);
>     a.foo(4);
> 
>     void delegate(int) dg;
>     dg.funcptr = &A.foo; // <<- dah
>     dg.ptr = cast(void*)a;

Are there other uses? Doesn't the above essentially boil down to just:

auto dg = &a.foo;

>     dg(8);
> }
> 

-- 
Remove ".doesnotlike.spam" from the mail address.

Deewiant wrote:
> Jarrett Billingsley wrote:
>  > It's a function pointer to that method.  It's actually useful -- you can
>> simulate pointer-to-members using this and delegates:
>>
>> class A
>> {
>>     int mX;
>>
>>     this(int x)
>>     {
>>         mX = x;
>>     }
>>
>>     void foo(int y)
>>     {
>>         writefln(mX, ", ", y);
>>     }
>> }
>>
>> void main()
>> {
>>     scope a = new A(5);
>>     a.foo(4);
>>
>>     void delegate(int) dg;
>>     dg.funcptr = &A.foo; // <<- dah
>>     dg.ptr = cast(void*)a;
> 
> Are there other uses? Doesn't the above essentially boil down to just:
> 
> auto dg = &a.foo;
> 

It does, except that you could later set dg.ptr to a /different/ instance.  Its utility is in late binding to instances selected by some arbitrary (and possibly external) means. I'd like to see if it plays well with inheritance, though.

-- Chris Nicholson-Sauls

Chris Nicholson-Sauls wrote:
> Deewiant wrote:
> 
>> Jarrett Billingsley wrote:
>>  > It's a function pointer to that method.  It's actually useful -- you can
>>
>>> simulate pointer-to-members using this and delegates:
>>>
>>> class A
>>> {
>>>     int mX;
>>>
>>>     this(int x)
>>>     {
>>>         mX = x;
>>>     }
>>>
>>>     void foo(int y)
>>>     {
>>>         writefln(mX, ", ", y);
>>>     }
>>> }
>>>
>>> void main()
>>> {
>>>     scope a = new A(5);
>>>     a.foo(4);
>>>
>>>     void delegate(int) dg;
>>>     dg.funcptr = &A.foo; // <<- dah
>>>     dg.ptr = cast(void*)a;
>>
>>
>> Are there other uses? Doesn't the above essentially boil down to just:
>>
>> auto dg = &a.foo;
>>
> 
> It does, except that you could later set dg.ptr to a /different/ instance.  Its utility is in late binding to instances selected by some arbitrary (and possibly external) means. I'd like to see if it plays well with inheritance, though.
> 
> -- Chris Nicholson-Sauls

It doesn't, really.

class Base {
    void foo() { writefln("Base"); }
}

class Derived : Base {
    void foo() { writefln("Derived"); }
}

void main() {
    void delegate() dg;
    dg.funcptr = &Base.foo;
    dg.ptr = new Derived;
    dg(); // will print "Base"
}

However, this is precisely the behavior I would expect, and in fact Pyd relies on it.

-- 
Kirk McDonald
http://kirkmcdonald.blogspot.com
Pyd: Connecting D and Python
http://pyd.dsource.org