使用 - >在模板中，以强制以下符号依赖 [英] Use of -> in a template in order to force the following symbol to be dependent

问题描述

从问题：

正确使用 - >

答案说明可以使用 - >

...在模板中，为了强制以下符号为
从属 - 在后面的使用，它通常是不可避免的。

这是什么意思，什么是这个用法的好例子？我不太明白依赖是什么意思，但它听起来像一个有用的技巧。

解决方案

问题：

 模板< class T> 
 struct foo：T {
 void bar（）{
 x = 5; // does not work 
 this-> x = 5; // works  -  T has a member x 
} 
}; 
  

没有 this-> 类似于使用 typename x / code>和模板内部模板代码：

 <类T，类S> 
 struct foo：T {
 typedef T :: ttype< S> ;; // does not work 
 typedef typename T :: template ttype< S> footype; // works 
}; 
  

这是愚蠢的，有点不必要，但你还是要这样做。

From the question:

Proper use of this->

The answer states that -> can be used

...in a template, in order to force the following symbol to be dependent—in this latter use, it is often unavoidable.

What does this mean what what would a good example of this use be? I don't quite what "dependent" means in this context, but it sounds like a useful trick.

解决方案

Posted in other question:

template <class T>
struct foo : T {
  void bar() {
    x = 5;       // doesn't work
    this->x = 5; // works - T has a member named x
  }
};

Without this-> compiler doesn't know x is a (inherited) member.

Similar to use of typename and template inside template code:

template <class T, class S>
struct foo : T {
  typedef T::ttype<S>; // doesn't work
  typedef typename T::template ttype<S> footype; // works
};

It's silly and somewhat unnecessary, but you still gotta do it.

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