c++ - boost 概念检查 operator() 重载

Question

template <typename T, typename C>
class CSVWriter{
    template <typename PrinterT>
    void write(std::ostream& stream, const PrinterT& printer){

    }
};

我想检查是否存在至少两个重载PrinterT::operator()(T*)，并且PrinterT::operator()(C*)
PrinterT可能会或可能不会继承std::unary_function
我需要在这里使用什么概念检查类？

（我没有使用 C++11）

Answer 1

你可以使用类似的东西

#include <iostream>

#include <boost/concept/requires.hpp>
#include <boost/concept/usage.hpp>

template <class Type, class Param>
class has_operator_round_brackets_with_parameter
{
public:
    BOOST_CONCEPT_USAGE(has_operator_round_brackets_with_parameter)
    {
        _t(_p);
    }

private:
    Type    _t;
    Param   _p;
};

struct X {};
struct Y {};

struct Test1
{
    void operator() (X*) const { }
};

struct Test2: public Test1
{
    void operator() (X*) const { }
    void operator() (Y*) const { }
};

template <class T, class C>
struct CSVWriter
{
    template <class PrinterT>
    BOOST_CONCEPT_REQUIRES(
        ((has_operator_round_brackets_with_parameter<PrinterT, T*>))
        ((has_operator_round_brackets_with_parameter<PrinterT, C*>)),
    (void)) write(std::ostream& stream, const PrinterT& printer)
    {

    }
};

int main()
{
    CSVWriter<X, Y> w;
    // w.write<Test1>(std::cout, Test1());  // FAIL
    w.write<Test2>(std::cout, Test2());     // OK
    return 0;
}