templates help

[lallous]

Hello,

I would like to define a template as:

template <class T, class R> void func(T &r)
{
r = (T)((R)r);
}

For example:
double d;
func<double, int>(d);
this would do: (double)((int)d )

1)Is this a good way to achieve this?
I don't want to use any instance of "R" but just use it to cast.

2)
How can I set that "R" is by default a "long" type?
It seems that <class T, class R = long> will only work w/ classes and not
function templates.

Regards,
Elias

[Victor Bazarov]

Re: templates help

"lallous" <lallous@lgwm.o rg> wrote...[color=blue]
> I would like to define a template as:
>
> template <class T, class R> void func(T &r)
> {
> r = (T)((R)r);
> }
>
> For example:
> double d;
> func<double, int>(d);
> this would do: (double)((int)d )
>
> 1)Is this a good way to achieve this?
> I don't want to use any instance of "R" but just use it to cast.[/color]

No, type casts cannot be used as a source of information for template
type derivation. You could do

template<class R, class T> void func(T &r)
{
r = T(R(r));
}

...
double d;
...
func<int>(d); // no need to declare 'T', it will be
// derived from the argument
[color=blue]
>
> 2)
> How can I set that "R" is by default a "long" type?
> It seems that <class T, class R = long> will only work w/ classes and not
> function templates.[/color]

I am not sure what you mean by "will only work". Default template
arguments are allowed for functions too.

Victor