Уточнение пространства имён enum-а

#cpp #ооп #классы

Почему для return type надо уточнить какой enum  

TestClass::ePower TestClass::GetPower()


, а для входного параметра нет?

void TestClass::SetPower( ePower _power )  


при написании реализации вне класса ?  



Весь hello world код:

#include 
using namespace std;

//////////////////////////////////////////////////////////////////////////

enum class ePower
{
   other,
};

//////////////////////////////////////////////////////////////////////////

class TestClass
{
public:
   enum class ePower
   {
      on,
      off
   };


private:
   ePower                                    power;

public:
   void                                      SetPower( ePower _power );
   ePower                                    GetPower();
};


////////////////////////////////////////////////////////////////////


void TestClass::SetPower( ePower _power )
{
   power = _power;
}


TestClass::ePower TestClass::GetPower()
{
   return power;
}


int main()
{
   TestClass a;
   a.SetPower( TestClass::ePower::on );
}

    

Ответы

Ответ 1

В соответствии с правилами поиска неквалифицированных имен, в частности, имена, используемые
вне декларатора функции-члена класса, как, например, используемые в описании возвращаемого
значения, ищутся в той области, где определен класс.

Имена, используемые в частности в деклараторе функции-члене класса, ищутся в области
определения класса. 

Поиск неквалифицированных имен для вашего примера описан в параграфах №7 и №8 раздела
3.4.1 Unqualified name lookup  стандарта C++.


  7 A name used in the definition of a class X outside of a member
  function body, default argument, exceptionspecification,
  brace-or-equal-initializer of a non-static data member, or nested
  class definition29 shall be declared in one of the following ways:
  
  — before its use in class X or be a member of a base class of X
  (10.2), or
  
  — if X is a nested class of class Y (9.7), before the definition of X
  in Y, or shall be a member of a base class of Y (this lookup applies
  in turn to Y ’s enclosing classes, starting with the innermost
  enclosing class),30 or
  
  — if X is a local class (9.8) or is a nested class of a local class,
  before the definition of class X in a block enclosing the definition
  of class X, or
  
  — if X is a member of namespace N, or is a nested class of a class
  that is a member of N, or is a local class or a nested class within a
  local class of a function that is a member of N, before the definition
  of class X in namespace N or in one of N ’s enclosing namespaces.


и


  8 For the members of a class X, a name used in a member function body,
  in a default argument, in an exceptionspecification, in the
  brace-or-equal-initializer of a non-static data member (9.2), or in
  the definition of a class member outside of the definition of X,
  following the member’s declarator-id31, shall be declared in one of the 
  following ways:
  
  — before its use in the block in which it is used or in an enclosing
  block (6.3), or
  — shall be a member of class X or be a member of a base class of X
  (10.2), or
  
  — if X is a nested class of class Y (9.7), shall be a member of Y, or
  shall be a member of a base class of Y (this lookup applies in turn to
  Y’s enclosing classes, starting with the innermost enclosing class),32
  or
  
  — if X is a local class (9.8) or is a nested class of a local class,
  before the definition of class X in a block enclosing the definition
  of class X, or
  
  — if X is a member of namespace N, or is a nested class of a class
  that is a member of N, or is a local class or a nested class within a
  local class of a function that is a member of N, before the use of the
  name, in namespace N or in one of N ’s enclosing namespaces.


И сноска 31


  31) That is, an unqualified name that occurs, for instance, in a
  type in the parameter-declaration-clause or in the
  exception specification.


Эти же правила дублируются и в других разделах, где описание относится к классам.