[英]C++ template how to overloading operator and accessing private property
I am currently trying to implement a simple template-based linked list that takes a generic key/value-pair in C++11. 我目前正在尝试实现一个简单的基于模板的链表,它在C ++ 11中采用通用键/值对。 Elements should be added to the list by the += operator.
元素应该由+ =运算符添加到列表中。 The code looks like this:
代码如下所示:
list 名单
// Forward declarations
template<typename K, typename V>
class list;
template<typename K, typename V>
list<K, V> &operator+=(list<K, V> &list, const std::tuple<K, V> ele) {
if (!list.head) {
// list is empty
list.head = new element(ele, nullptr);
}
return list;
};
// Class definition
template<typename K, typename V>
class list {
private:
struct element {
const K key;
const V value;
element *next;
element(const std::tuple<K, V> tuple, element *ele) :
key(std::get<0>(tuple)),
value(std::get<1>(tuple)),
next(ele) { }
};
element *head = nullptr;
public:
friend list<K, V> &operator+=<>(list<K, V> &list, const std::tuple<K, V> ele);
};
I can't get this to compile. 我无法编译。 Do I have to put the implementation of the operator into the forward declaration or into the class itself?
我是否必须将运算符的实现放入前向声明或类本身? If I put it in the forward-declaration, like in the snippet, I can't seem to use "list.head = new element(ele, nullptr);".
如果我把它放在前向声明中,就像在片段中一样,我似乎无法使用“list.head = new element(ele,nullptr);”。 Error: expected type-specifier before 'element'
错误:'element'之前的预期类型说明符
If I put it into the class itself, I can't access list.head even tho it's a friend. 如果我将它放入课堂本身,我就无法访问list.head,即使它是朋友。
You should just leave the declaration of the function template before the class template definition (after the forward declaration), to tell the compiler that operator+=
specified in the friend declaration is a template. 您应该在类模板定义之前(在前向声明之后)保留函数模板的声明,以告诉编译器在friend声明中指定的
operator+=
是模板。 Then define it later. 然后再定义它。 eg
例如
// Forward declarations
template<typename K, typename V>
class list;
// declaration of function template
template<typename K, typename V>
list<K, V> &operator+=(list<K, V> &l, const std::tuple<K, V> ele);
// Class definition
template<typename K, typename V>
class list {
...
friend list<K, V> &operator+=<>(list<K, V> &l, const std::tuple<K, V> ele);
};
// definition of function template
template<typename K, typename V>
list<K, V> &operator+=(list<K, V> &l, const std::tuple<K, V> ele) {
if (!l.head) {
// list is empty
l.head = new typename list<K, V>::element(ele, nullptr);
}
return l;
}
PS: PS:
Don't name the parameter with the name list
, which conflicts with the name of class template list
. 不要使用名称
list
命名参数,该list
与类模板list
的名称冲突。
element
is a nested struct, in operator+=
you should specify it like typename list<K, V>::element
. element
是一个嵌套的struct,在operator+=
你应该像typename list<K, V>::element
一样指定它。
Using name list
(same as std::list
) is not a good idea. 使用名称
list
(与std::list
相同)不是一个好主意。
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