A partial specialization of a class template provides an alternative definition
of the template that is used instead of the primary definition when the
arguments in a specialization match those given in the partial
specialization (
[temp.class.spec.match])
.The primary template shall be declared before any specializations of
that template
.A partial specialization shall be declared before the first use of a class template
specialization that would make use of the partial specialization as the result of
an implicit or explicit instantiation in every translation unit in which such a use
occurs; no diagnostic is required
. The template parameters are specified in the angle bracket enclosed list
that immediately follows the keyword
template.For partial specializations, the template argument list is explicitly
written immediately following the class template name
.For primary templates, this list is implicitly described by the
template parameter list
.Specifically, the order of the template arguments is the sequence in
which they appear in the template parameter list
.[
Example 3: The template argument list for the primary template in the example
above is
<T1,
T2,
I>. —
end example]
[
Note 1: The template argument list cannot be specified in the primary template
declaration
.For example,
template<class T1, class T2, int I>
class A<T1, T2, I> { };
—
end note]
Partial specialization declarations themselves are not found by name lookup
.Rather, when the primary template name is used, any previously-declared partial
specializations of the primary template are also considered
.One consequence is
that a
using-declaration
which refers to a class template does not restrict the set of partial specializations
which may be found through the
using-declaration.[
Example 5: namespace N {
template<class T1, class T2> class A { };
}
using N::A;
namespace N {
template<class T> class A<T, T*> { };
}
A<int,int*> a;
—
end example]