c_cpp 另一个使用c ++ 11和可变参数模板的代理

Posted 2021-05-14

#ifndef _DELEGATE_H_
#define _DELEGATE_H_

/**
 * non specialized template declaration for delegate
 */
template <typename T>
class delegate;

/**
 * specialization for member functions
 *
 * \tparam T            class-type of the object who's member function to call
 * \tparam R            return type of the function that gets captured
 * \tparam params       variadic template list for possible arguments
 *                      of the captured function
 */
template <typename T, typename R, typename... Params>
class delegate<R (T::*)(Params...)>
{
public:
    typedef R (T::*func_type)(Params...);

    delegate(func_type func, T& callee)
        : callee_(callee)
        , func_(func)
    {}

    R operator()(Params... args) const
    {
        return (callee_.*func_)(args...);
    }

    bool operator==(const delegate& other) const
    {
        return (&callee_ == &other.callee_) && (func_ == other.func_);
    }
    bool operator!= (const delegate& other) const
    {
        return !((*this) == other);
    }

private:
    T& callee_;
    func_type func_;
};

/**
 * specialization for const member functions
 */
template <typename T, typename R, typename... Params>
class delegate<R (T::*)(Params...) const>
{
public:
    typedef R (T::*func_type)(Params...) const;

    delegate(func_type func, const T& callee)
        : callee_(callee)
        , func_(func)
    {}

    R operator()(Params... args) const
    {
        return (callee_.*func_)(args...);
    }

    bool operator==(const delegate& other) const
    {
        return (&callee_ == &other.callee_) && (func_ == other.func_);
    }
    bool operator!= (const delegate& other) const
    {
        return !(*this == other);
    }

private:
    const T& callee_;
    func_type func_;
};

/**
 * specialization for free functions
 *
 * \tparam R            return type of the function that gets captured
 * \tparam params       variadic template list for possible arguments
 *                      of the captured function
 */
template <typename R, typename... Params>
class delegate<R (*)(Params...)>
{
public:
    typedef R (*func_type)(Params...);

    delegate(func_type func)
        : func_(func)
    {}

    R operator()(Params... args) const
    {
        return (*func_)(args...);
    }

    bool operator==(const delegate& other) const
    {
        return func_ == other.func_;
    }
    bool operator!= (const delegate& other) const
    {
        return !((*this) == other);
    }

private:
    func_type func_;
};

/**
 * function to deduce template parameters from call-context
 */
template <typename F, typename T>
delegate<F> make_delegate(F func, T& obj)
{
    return delegate<F>(func, obj);
}

template <typename T>
delegate<T> make_delegate(T func)
{
    return delegate<T>(func);
}

// a little backward compatilbility layer
#define DELEGATE make_delegate
#define DELEGATE_CONST make_delegate
#define DELEGATE_FREE make_delegate

#endif /* end of include guard */

#include <iostream>

#include "delegate.hpp"

class A
{
public:
    void deadSimple()
    {
        printf("no params whatsoever\n");
    }
    int foo(int x)
    {
        return x*x;
    }
    int bar(int x, int y, char a)
    {
        return a == 'a' ? x+y : x*y;
    }
    void crazy(int I, char wanna, float go, const char* crazy)
    {
        printf("I=%d, wanna=%c, go=%f, crazy=%s\n",
               I, wanna, go, crazy);
    }
};
int main()
{
    A a;
    auto d = DELEGATE(&A::foo, a);
    auto d2 = DELEGATE(&A::bar, a);
    auto d3 = DELEGATE(&A::crazy, a);
    auto d4 = DELEGATE(&A::deadSimple, a);
    printf("d(42)=%d\n", d(42));
    printf("d2(42, 2, 'a')=%d\n", d2(42, 2, 'a'));
    const char* s = "sheeeet!";
    d3(5, 'a', 4.5, s);
    d4();
    return 0;
}