Re: template parameter not used in partial specialization

From:

=?ISO-8859-1?Q?Daniel_Kr=FCgler?= <daniel.kruegler@googlemail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 26 Feb 2013 05:13:28 CST

Message-ID:

<kghp46$v4i$1@dont-email.me>

On 2013-02-26 02:27, Daniel Kr?gler wrote:

Am 25.02.2013 21:44, schrieb Walter Mascarenhas:

The code below does not compile in g++ 4.7.2: it says
that the template parameter S is not used in Foo's
specialization below. Is g++ correct on this? If so,
how would I specialize the struct Foo for
T = std::vector<S>::iterator in a general way?

#include <vector>
template <typename T>
struct Foo
{
};

template <typename S>
struct Foo< typename std::vector<S>::iterator >
{
};

Yes, the code is ill-formed, no diagnostic required.

I should add here that your example is covered by an existing core
language issue:

http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#549

The current wording is astonishing unclear in regard to the diagnostic
requirements in this case. Personally I expect that in the end a
diagnostic will be required here, since it is similar to non-deduced
contexts for functions templates (as described in my example).

HTH & Greetings from Bremen,

Daniel Kr?gler

--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]