Topic: Member function template explicit specializations.
Author: wmm@fastdial.net (William M. Miller)
Date: Wed, 28 Mar 2001 12:47:53 CST Raw View
[posted and mailed]
kavdeiv@mail.ru ("Kiril Avdeiv") wrote in <E14gBpT-000MSk-00@f12.port.ru>:
>I've been reading and rereading the piece 14.7.3/18:
>
>"In an explicit specialization declaration for a member of a class
template or a member template that appears in namespace scope, the member
template and some of its enclosing class templates may remain
unspecialized, except that the declaration shall not explicitly specialize
a class member template if its enclosing class templates are not explicitly
specialized as well. In such explicit specialization declaration, the
keyword template followed by a template-parameter-list shall be provided
instead of the template<> preceding the explicit specialization declaration
of the member...".
>
>For brevity's sake, lets restrict the discussion to cases when there's a
class template with a nested member class template and a member function
template.
>
>While it's clear that you cannot explicitly specialize a member class
template without explicitly specializing the enclosing class, I'm not sure
that the above paragraph renders constructs like the one below semantically
incorrect:
>
>template<class T1>
>class A {
> template<class T2>
> class B {
> };
> template<class T2>
> void foo(T2 param) {}
>};
>template<class T1> template<>
>void A<T1>::foo(long double param) {}
>
>In fact, I read it as allowing for it.
>
>Can anybody from the the standardization committee elucidate the meaning
of the paragraph please?
That wording is very unclear because there are _two_ (or more)
"template" keywords in such a declaration. However, the one it
is referring to is the one associated with the nested member, not
with the containing class template. In your example, it's saying
that the "template<>" you use as the introducer for "foo" must be
a regular template argument list instead.
(If I misunderstood your question, please let me know.)
--
William M. Miller, wmm@fastdial.net
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Author: kavdeiv@mail.ru (\"Kiril Avdeiv\")
Date: Thu, 22 Mar 2001 21:57:15 GMT Raw View
I've been reading and rereading the piece 14.7.3/18:
"In an explicit specialization declaration for a member of a class template or a member template that appears in namespace scope, the member template and some of its enclosing class templates may remain unspecialized, except that the declaration shall not explicitly specialize a class member template if its enclosing class templates are not explicitly specialized as well. In such explicit specialization declaration, the keyword template followed by a template-parameter-list shall be provided instead of the template<> preceding the explicit specialization declaration of the member...".
For brevity's sake, lets restrict the discussion to cases when there's a class template with a nested member class template and a member function template.
While it's clear that you cannot explicitly specialize a member class template without explicitly specializing the enclosing class, I'm not sure that the above paragraph renders constructs like the one below semantically incorrect:
template<class T1>
class A {
template<class T2>
class B {
};
template<class T2>
void foo(T2 param) {}
};
template<class T1> template<>
void A<T1>::foo(long double param) {}
In fact, I read it as allowing for it.
Can anybody from the the standardization committee elucidate the meaning of the paragraph please?
Thank you in advance.
Kiril.
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Author: "Victor Bazarov" <vAbazarov@dAnai.com>
Date: Thu, 22 Mar 2001 22:23:49 GMT Raw View
""Kiril Avdeiv"" <kavdeiv@mail.ru> wrote...
> I've been reading and rereading the piece 14.7.3/18:
>
> "In an explicit specialization declaration for a member of a class
template or a member template that appears in namespace scope, the
member template and some of its enclosing class templates may remain
unspecialized, except that the declaration shall not explicitly
specialize a class member template if its enclosing class templates are
not explicitly specialized as well. In such explicit specialization
declaration, the keyword template followed by a template-parameter-list
shall be provided instead of the template<> preceding the explicit
specialization declaration of the member...".
>
> For brevity's sake, lets restrict the discussion to cases when there's
a class template with a nested member class template and a member
function template.
>
> While it's clear that you cannot explicitly specialize a member class
template without explicitly specializing the enclosing class, I'm not
sure that the above paragraph renders constructs like the one below
semantically incorrect:
>
> template<class T1>
> class A {
> template<class T2>
> class B {
> };
> template<class T2>
> void foo(T2 param) {}
> };
> template<class T1> template<>
> void A<T1>::foo(long double param) {}
>
> In fact, I read it as allowing for it.
>
> Can anybody from the the standardization committee elucidate the
meaning of the paragraph please?
Right away: I am not from the Committee, I only have one extra
question.
I always thought that when one defined a member template, the
"template<...>" for it was sort of _enclosing_ the outer class
or template. So, what I learned is that a correct way of
defining the foo specialization would be
template<> template<class T1>
void A<T1>::foo(long double param) {}
Is there really any difference? Or do I simply know it wrong?
Thank you.
Victor
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