Question

这是ISO C ++标准14.6.2.1的声明：依赖类型：

A type is dependent if it is
— a template parameter,#1
— a qualified-id with a nested-name-specifier which contains a class-name
   that names a dependent type or whose unqualified-id names a dependent type,#2
— a cv-qualified type where the cv-unqualified type is dependent, #3
— a compound type constructed from any dependent type,#4
— an array type constructed from any dependent type or whose size is specified
    by a constant expression that is value-dependent, #5
— a template-id in which either the template name is a template parameter
   or any of the template arguments is a dependent type or an expression 
   that is type-dependent or value-dependent.#6

我无法理解最后两点？

任何人都可以举例说明这些陈述（尤其是最后的＃5，＃6）？

Answer 1

从1) a type is dependent if it is a template parameter开始工作：

template <typename T, int N, template <typename> class My_Template>
struct X
{

5 - 从任何依赖类型构造的数组类型，或者其大小由与值相关的常量表达式指定，

    T a[5];        // array of dependent type
    int b[N];      // value-dependent size

6 - 模板ID，其中模板名称是模板参数
或任何模板参数是依赖类型或表达式这是依赖于类型或依赖于价值的。

    My_Template<int> c;           // template parameter
    Some_Template<T> d;           // template argument is dependent
    Another_Template<sizeof c> e; // type-dependent expression
    Another_Template<N> f;        // value-dependent expression
};

Answer 2

template<class T> struct Base{ 
}; 

template<class T, int n, template<class X> class U> struct Derived : Base<T>{ 
    T array1[10];       // #5 

    int array2[n];      // #5 

    U<T> u;             // #6 
    Base<T> b;          // #6 
}; 


int main(){}

模板：名称解析：依赖类型： - ＆gt;任何人都可以为此声明说明更多示例吗？

2 个答案: