初始化和访问可变类类模板的成员 [英] Initialzing and accessing members of a variadic class template

问题描述

我正在尝试可变参数模板，并想知道是否可以使用它们为了generalze（？）类模板，如

  template< typename T1，typename T2，typename T4，typename T4> 
 struct Foo 
 {
 T1& m_member1; 
 T2& m_member2; 
 T3& m_member3; 
 T4& m_member4; 
}; 
  

此外，我想能够通过链接构造函数初始化所有成员。这是我到多远：

 模板< typename ... Types> 
 struct Foo; 
 
 template< typename T，typename ... Types> 
 struct Foo< T，Types ...> ：public Foo< Types ...> 
 {
 Foo（T member，Types ... others）：m_member（member），Foo< Types ...>（others）
 {
} 
 
 T m_member; 
}; 
 
 template< typename T> 
 struct Foo< T> 
 {
 Foo（T member）：m_member（member）
 {
} 
 
 T m_member; 
}; 
  

目标是创建如下对象：

  Foo< char，int，bool，float> f（'a'，42，true，1.234）; 
  

代码无法编译（gcc 4.5.3）时出现错误：

  TestVariadicTemplates.cpp：在构造函数'Foo< T，Types ...> :: Foo（T，Types ...）'：
 TestVariadicTemplates.cpp：15：83：error：参数包不用'...'扩展：
 TestVariadicTemplates.cpp：15：83：note：'others'
 TestVariadicTemplates.cpp：15：困惑的早期错误，bumb out 
  
 
 
 
 编辑 
 $ b 
最好的方法是引用 Foo 的各个成员？ 
解决方案
您必须说明：使用<$ c $展开来自参数包（变量参数）的变量c> ... 。
 
 
 
也就是说，而不是
  Foo   
 
 
 
  Foo< Types ...>（others ...）
  
 
I'm experimenting with variadic templates and would like to know if they can be used in order to generalze(?) class templates such as
template<typename T1, typename T2 , typename T4, typename T4>
struct Foo
{
    T1      &m_member1;
    T2      &m_member2;
    T3      &m_member3;
    T4      &m_member4;
};
Also, I'd like to be able to initialize all the members by chaining constructors. This is how far I've gotten:
template<typename... Types>
struct Foo;

template<typename T , typename... Types>
struct Foo<T, Types ...> : public Foo<Types ...>
{
    Foo( T member , Types ... others ) : m_member( member ) , Foo<Types ...>( others )
    {
    }

    T   m_member;
};

template<typename T>
struct Foo<T>
{
    Foo( T member ) : m_member( member )
    {
    }

    T   m_member;
};
Where the goal is to create objects like so:
Foo<char,int,bool,float> f( 'a' , 42 , true , 1.234 );
The code fails to compile (gcc 4.5.3) with the error:
TestVariadicTemplates.cpp: In constructor ‘Foo<T, Types ...>::Foo(T, Types ...)’:
TestVariadicTemplates.cpp:15:83: error: parameter packs not expanded with ‘...’:
TestVariadicTemplates.cpp:15:83: note:         ‘others’
TestVariadicTemplates.cpp:15: confused by earlier errors, bailing out
Edit

What would be the best way to reference the various members of Foo? 
解决方案
You have to do what it says: Expand the variables that come from Parameter packs (variadic parameters) with ....

That is, instead of
Foo<Types ...>( others )
write
Foo<Types ...>( others... )


                        
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