c++模板[]重载

Question

我有一个类，它具有括号运算符的模板函数。它可以编译，但我不知道如何访问它。

见下面的例子：

   class Test {
    public:
        template <class T> pServiceState operator[] (const std::string project) {
             return getService<T>(project);
        }

       template <class T> pServiceState getService(const std::string project) {
             pService s = get_service<T>();
             if(s == NULL) throw "Service does not exist on server";
             return s->state(project);
        }

    }

int main(){

    states.getService<content_uploader>("asd"); // Works
    states<content_uploader>["asd"]; // Throws syntax errors.

/*
error: expected primary-expression before ‘>’ token
error: expected primary-expression before ‘[’ token
*/


}

感谢您的帮助， 亚当

Answer 1

编译器无法从您的案例中的参数派生模板参数T，因此您需要指定它。语法类似于常规函数。所以，试试：states.operator[]<content_uploader>("asd")

例子：

#include <iostream>
#include <vector>

class Foo
{
public:
    Foo() : vec(5, 1) {}
    template <typename T>
    int operator[](size_t index)
    {
        std::cout << "calling [] with " << index << std::endl;
        return vec[index];
    }
private:
    std::vector<int> vec;
};

int main()
{
    Foo foo;
    foo.operator[]<int>(2);
}