13 Templates [temp]

13.6 Type equivalence [temp.type]

Two template-ids refer to the same class, function, or variable if
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,133 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,134 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
:
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
:
However, such a type may be aliased, e.g., by a typedef-name.
— end note
 ]
The identity of enumerators is not preserved.
An array as a template-parameter decays to a pointer.