mem_fun_ref

[Anders]

Hello.
If I was to call a method of class T, M for each element in a collection,
I'd do it like this:

vector<int> vec;
....
for_each(vec.be gin(), vec.end(), mem_fun_ref(&T: :M));

Okay, I can see that mem_fun_REF makes it obvious that I must use a
reference, but why? Is it not possible to pass a function by-reference? As I
see it, T::M is being passed as a pointer here.

void func(int& val); func(12); << reference
void func(int* val); int val = 12; func(&val); << pointer

//Anders

[Kurt Krueckeberg]

Re: mem_fun_ref

[color=blue]
> Hello.
> If I was to call a method of class T, M for each element in a collection,
> I'd do it like this:
>
> vector<int> vec;
> ...
> for_each(vec.be gin(), vec.end(), mem_fun_ref(&T: :M));
>
> Okay, I can see that mem_fun_REF makes it obvious that I must use a
> reference, but why? Is it not possible to pass a function by-reference?[/color]

No, you can only pass the address.[color=blue]
> As I see it, T::M is being passed as a pointer here.[/color]

The REF, in mem_fun_ref, refers to the argument type( of T::M ), which
will be passed to the function call operator.[color=blue]
>
> void func(int& val); func(12); << reference
> void func(int* val); int val = 12; func(&val); << pointer
>
> //Anders
>
>[/color]

[tom_usenet]

Re: mem_fun_ref

On Mon, 30 Jun 2003 22:34:24 +0200, "Anders" <gregersen@adsl home.dk>
wrote:
[color=blue]
>Hello.
>If I was to call a method of class T, M for each element in a collection,
>I'd do it like this:
>
>vector<int> vec;
>...
>for_each(vec.b egin(), vec.end(), mem_fun_ref(&T: :M));[/color]

That can't be legal - you can't call a T member function on an int
reference.
[color=blue]
>
>Okay, I can see that mem_fun_REF makes it obvious that I must use a
>reference, but why? Is it not possible to pass a function by-reference? As I
>see it, T::M is being passed as a pointer here.
>
>void func(int& val); func(12); << reference
>void func(int* val); int val = 12; func(&val); << pointer[/color]

The ref refers to the the fact that the object passed as the first
argument of the functor must be a reference. e.g.

T t;

mem_fun_ref(&T: :M)(t); //pass T reference

mem_fun(&T::M)( &t); //pass T pointer

so in practice you use mem_fun_ref for containers like:
vector<T>
and mem_fun for containers like:
vector<T*>

Tom