13 Templates [temp]

The template parameters of a template are specified in the angle bracket enclosed list that immediately follows the keyword template.

A primary template declaration is one in which the name of the template is not followed by a template-argument-list.

The template argument list of a primary template is the template argument list of its template-head ([temp.arg]).

A template declaration in which the name of the template is followed by a template-argument-list is a partial specialization ([temp.spec.partial]) of the template named in the declaration, which shall be a class or variable template.

For purposes of name lookup and instantiation, default arguments, type-constraints, requires-clauses ([temp.pre]), and noexcept-specifiers of function templates and of member functions of class templates are considered definitions; each default argument, type-constraint, requires-clause, or noexcept-specifier is a separate definition which is unrelated to the templated function definition or to any other default arguments, type-constraints, requires-clauses, or noexcept-specifiers.

For the purpose of instantiation, the substatements of a constexpr if statement are considered definitions.

For the purpose of name lookup and instantiation, the compound-statement of an expansion-statement is considered a template definition.

Because an alias-declaration cannot declare a template-id, it is not possible to partially or explicitly specialize an alias template.