Prev: check file opened or not?
Next: Init COM interfaces
From: Jack Hanebach on 2 Apr 2008 13:16

Given:

template<typename T1, typename T2>
struct A
{
void foo() {}
};

we can specialize the A::foo() as follow:

template<>
void A<double, int>::foo()
{
}

or we can partially specialize A

template<typename T>
struct A<T, double>
{
void foo() {}
};

Yet, according to VC8 and comeau, we cannot partially
specialize A::foo() like that:

template<typename T>
void A<T, double>::foo() {}

Am I using the incorrect syntax, or is that kind of partial
specialization illegal? If so, anybody has any Idea why?

// since I need special behavior for only one method,
// I don't really want to specialize the whole class
// and have to 'copy and paste' the other methods...
From: Ben Voigt [C++ MVP] on 2 Apr 2008 13:45
Jack Hanebach wrote:
> Given:
>
> template<typename T1, typename T2>
> struct A
> {
> void foo() {}
> };
>
> we can specialize the A::foo() as follow:
>
> template<>
> void A<double, int>::foo()
> {
> }
>
> or we can partially specialize A
>
> template<typename T>
> struct A<T, double>
> {
> void foo() {}
> };
>
> Yet, according to VC8 and comeau, we cannot partially
> specialize A::foo() like that:
>
> template<typename T>
> void A<T, double>::foo() {}
>
> Am I using the incorrect syntax, or is that kind of partial
> specialization illegal? If so, anybody has any Idea why?
>
> // since I need special behavior for only one method,
> // I don't really want to specialize the whole class
> // and have to 'copy and paste' the other methods...

Inheritance often helps reuse the same behavior in several partial
specializations.


From: Victor Bazarov on 2 Apr 2008 13:40
Jack Hanebach wrote:
> [..]
> Am I using the incorrect syntax, or is that kind of partial
> specialization illegal? If so, anybody has any Idea why?

Partial specialisations of functions are prohibited.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask


From: Jack Hanebach on 2 Apr 2008 13:55
Ben Voigt [C++ MVP] wrote:

> Inheritance often helps reuse the same behavior in several partial
> specializations.

Yes, I know. Actually that's how I solved my problem. By factoring the
original design into 'policy' classes.

I was just curious what might be the reason for disallowing
what is essentially just a shortcut for partial specialization of the
class, when we neeed changed behavior in only some methods.

--

From: Igor Tandetnik on 2 Apr 2008 22:21
"Jack Hanebach" <firstname(a)lastname.net> wrote in message
news:u53ZcVOlIHA.4712(a)TK2MSFTNGP04.phx.gbl
> Given:
>
> template<typename T1, typename T2>
> struct A
> {
> void foo() {}
> };
>
>
> Yet, according to VC8 and comeau, we cannot partially
> specialize A::foo() like that:
>
> template<typename T>
> void A<T, double>::foo() {}

There ain't no such thing as partial specialization of function
templates. You can simulate it by delegating to a class template, which
in turn can be partially specialized:

template <typename T1, typename T2>
struct FooImpl {
static void foo(A* pThis) {};
};

template<typename T1, typename T2>
struct A
{
void foo() { FooImpl<T1, T2>::foo(this); }
};

// Partial specialization
template<typename T>
struct FooImpl<T, double>
{
static void foo(A* pThis) {}
};

--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925


 |  Next  |  Last
Pages: 1 2 3 4
Prev: check file opened or not?
Next: Init COM interfaces