13 Templates [temp]

13.6 Type equivalence [temp.type]

Two template-ids are the same if
Two template-ids that are the same refer to the same class, function, or variable.
Two values are template-argument-equivalent if they are of the same type and
  • they are of integral type and their values are the same, or
  • they are of floating-point type and their values are identical, or
  • they are of type std​::​nullptr_­t, or
  • they are of enumeration type and their values are the same,136 or
  • they are of pointer type and they have the same pointer value, or
  • they are of pointer-to-member type and they refer to the same class member or are both the null member pointer value, or
  • they are of reference type and they refer to the same object or function, or
  • they are of array type and their corresponding elements are template-argument-equivalent,137 or
  • they are of union type and either they both have no active member or they have the same active member and their active members are template-argument-equivalent, or
  • they are of class type and their corresponding direct subobjects and reference members are template-argument-equivalent.
[Example 1:
template<class E, int size> class buffer { /* ... */ }; buffer<char,2*512> x; buffer<char,1024> y; declares x and y to be of the same type, and template<class T, void(*err_fct)()> class list { /* ... */ }; list<int,&error_handler1> x1; list<int,&error_handler2> x2; list<int,&error_handler2> x3; list<char,&error_handler2> x4; declares x2 and x3 to be of the same type.
Their type differs from the types of x1 and x4.
template<class T> struct X { }; template<class> struct Y { }; template<class T> using Z = Y<T>; X<Y<int> > y; X<Z<int> > z; declares y and z to be of the same type.
— end example]
If an expression e is type-dependent, decltype(e) denotes a unique dependent type.
Two such decltype-specifiers refer to the same type only if their expressions are equivalent ([temp.over.link]).
[Note 1:
However, such a type might be aliased, e.g., by a typedef-name.
— end note]
136)136)
The identity of enumerators is not preserved.
137)137)
An array as a template-parameter decays to a pointer.