newbie wrote:
>> same solution as befor (the issue is that the only thing you can put after
>> the '=' ouside of a function is a constant expression and a function litteral
>> isn't one)
> 
> Why a function literal is not a constant expression?
> 
> Especially after I defining a global top level wrapper function in this case.
> Under the hood, it should just be a raw pointer to some memory address, why this
> cannot be a constant?
> 
>> //at global scope (OTOH static's are globals)
>> static invariant FP mfp1;
>> static this()
>> {
>> mfp1 = cast(invariant FP)(function void(A obj){obj.f();});
>> }
> 
> Thanks again. I can live with this workaround right now, but I'd really like to
> write it as simple as:
> 
> invariant FP mfp2 = function void(A obj) {obj.f();};  // without the cast
> 
>> I still don't get it, what type of manipulation (outside self modifying code)
> 
> E.g. save in a hash-table, or use them as keys ...
> 
> And I'd really like to do self modifying code ;-) I read somewhere that D plan
> have to AST macros? so we are closer to lisp:
> http://en.wikipedia.org/wiki/Greenspun%27s_Tenth_Rule
> 
>> can you do that doesn't allow switching in a different function with the
>> same signature?
> 
> Yes, I do it manually (by writing program carefully). I want the help from the
> type system (or the language compiler) to protect me from such violation.
> 

I'm not sure I completely understand either but I'll take a stab.  What about using polymorphism?  Where delegates can be any type of object interfaces restrict what sort of objects can be used with your hash-table.

-Joel

> Do you want nothing at all to be assigname to the variable after the fist
> assigment?
> class Bob {void a(){} void b(){} }
> The_Type fnp = Bob.a;
> fnp = Bob.a; // valid or not?

Can fnp be invoked on an actual object? and what's the syntax?

Bob bob = new Bob();
fnp(bob);  // ? how to make this call?

> Do you care if other instances of the same type have pointers to other function? The_Type fnp = Bob.a;

> I'm not sure I completely understand either but I'll take a stab.  What about using polymorphism?  Where delegates can be any type of object interfaces restrict what sort of objects can be used with your hash-table.

Go back to my original question:

How to create a variable which hold a particular function pointer of a class, and can be invoked on different objects of that class:

fp = &(A.f);
A a1, a2;
a1.fp();   // how to make this invocation work?
a2.fp();

And I have one more requirement that even if A.f() and A.g() have same signature,

fp = &(A.g);   // expect compiler report error here.

How to declare the type of such fp?

u wrote:
>>I'm not sure I completely understand either but I'll take a stab.  What
>>about using polymorphism?  Where delegates can be any type of object
>>interfaces restrict what sort of objects can be used with your hash-table.
> 
> 
> Go back to my original question:
> 
> How to create a variable which hold a particular function pointer of a class, and
> can be invoked on different objects of that class:
> 
> fp = &(A.f);
> A a1, a2;
> a1.fp();   // how to make this invocation work?
> a2.fp();
> 
> And I have one more requirement that even if A.f() and A.g() have same signature,
> 
> fp = &(A.g);   // expect compiler report error here.
> 
> How to declare the type of such fp?

There is a current thread in digitalmars.D.learn titled "Pointer to member variable again." It has turned into a discussion of this very topic.

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

== Quote from Kirk McDonald (kirklin.mcdonald@gmail.com)'s article
> u wrote:
> > Go back to my original question:
> >
> > How to create a variable which hold a particular function pointer of a class, and can be invoked on different objects of that class:
> >
> > fp = &(A.f);
> > A a1, a2;
> > a1.fp();   // how to make this invocation work?
> > a2.fp();
> >
> > And I have one more requirement that even if A.f() and A.g() have same signature,
> >
> > fp = &(A.g);   // expect compiler report error here.
> >
> > How to declare the type of such fp?
> There is a current thread in digitalmars.D.learn titled "Pointer to
> member variable again." It has turned into a discussion of this very topic.

I had hoped that D will offer better solution than C++'s member function pointer.

Looks like currently it's more difficulty to do what I want in D.

Probably I will live with the wrapper function for now.

u wrote:
>> I'm not sure I completely understand either but I'll take a stab.  What
>> about using polymorphism?  Where delegates can be any type of object
>> interfaces restrict what sort of objects can be used with your hash-table.
> 
> Go back to my original question:
> 
> How to create a variable which hold a particular function pointer of a class, and
> can be invoked on different objects of that class:
> 
> fp = &(A.f);
> A a1, a2;
> a1.fp();   // how to make this invocation work?
> a2.fp();
> 
> And I have one more requirement that even if A.f() and A.g() have same signature,
> 
> fp = &(A.g);   // expect compiler report error here.
> 
> How to declare the type of such fp?

//What about something like:

void funcBind(Obj, alias Func)(Obj obj)
{
   obj.Func();
}

...

alias funcBind!(A, f) fp;
A a1, a2;
fp(a1);
fp(a2);


alias funcBind!(A, g) fp;  //Compiler error -> Duplicate

//Note with a little more work you could make A implicit
//and therefore have any class Type as the first parameter.

I can't really see why function/member pointers are necessary for this situation since Member pointers are one to many and you seem to want a one-to-one relationship.


-Joel

Reply to u,

>> Do you want nothing at all to be assigname to the variable after the
>> fist
>> assigment?
>> class Bob {void a(){} void b(){} }
>> The_Type fnp = Bob.a;
>> fnp = Bob.a; // valid or not?
> Can fnp be invoked on an actual object? and what's the syntax?
> 

the whole thing is hypothetical so ...

> Bob bob = new Bob();
> fnp(bob);  // ? how to make this call?
>> Do you care if other instances of the same type have pointers to
>> other function? The_Type fnp = Bob.a;
>>