template <class Ret, class... Args>
class function<Ret(Args...)>;

#include <iostream>
#include <functional>
using namespace std;
int add(int a, int b)
{
	return a + b;
}
int main()
{
	//包裝add函數(shù)，類(lèi)型匹配int<int, int>
	function<int(int, int)> func_add = add;
	cout << "1 + 2 = " << func_add(1, 2) << endl;
	return 0;
}

#include <iostream>
#include <functional>
using namespace std;
struct Sub {
	int operator()(int a, int b)
	{
		return a - b;
	}
};
int main()
{
	function<int(int, int)> func_sub = Sub();
	cout << "5 - 3 = " << func_sub(5, 3) << endl;
	return 0;
}

#include <iostream>
#include <functional>
using namespace std;
int main()
{
	function<int(int, int)> func_mul = [](int a, int b) {return a * b;};
	cout << "3 * 4 = " << func_mul(3, 4) << endl;
	return 0;
}

#include <iostream>
#include <functional>
using namespace std;
class Divide {
public:
	//非靜態(tài)成員函數(shù)，參數(shù)隱含this指針
	double div(double a, double b)
	{
		return a / b;
	}
	//靜態(tài)成員函數(shù)，不含this指針
	static double div_static(double a, double b)
	{
		return a / b;
	}
};
int main()
{
	Divide d;
	//包裝非靜態(tài)成員函數(shù)，包含this指針
	function<double(Divide*, double, double)> func_div = &Divide::div;//非靜態(tài)成員函數(shù)必須取地址，不能隱式類(lèi)型轉(zhuǎn)換
	cout << "func_div: " << "12.2 / 2 = " << func_div(&d, 12.2, 2) << endl;
	//包裝靜態(tài)成員函數(shù)，不包含this指針
	function<double(double, double)> func_stat_div = Divide::div_static;//取地址可加可不加
	cout << "func_stat_div: " << "12.2 / 2 = " << func_stat_div(12.2, 2) << endl;
	return 0;
}

#include <iostream>
#include <functional>
using namespace std;
int main()
{
	function<int(int, int)> func_empty;
	try {
		func_empty(3, 4);
	}
	catch (const bad_function_call& e) {
		cout << "error: " << e.what() << endl;
	}
	return 0;
}

//simple(1)	
template <class Fn, class... Args>
  /* unspecified */ bind (Fn&& fn, Args&&... args);
//with return type (2)	
template <class Ret, class Fn, class... Args>
  /* unspecified */ bind (Fn&& fn, Args&&... args);

#include <iostream>
#include <functional>
using namespace std;
using namespace placeholders;
int mul(int a, int b)
{
	return a * b;
}
int main()
{
	//綁定_a == 100, 新函數(shù)第一個(gè)參數(shù)_1傳給b
	auto mul_fixed_a = bind(mul, 100, _1);
	cout << "100 * 5 = " << mul_fixed_a(5) << endl;
	////綁定_b == 200, 新函數(shù)第一個(gè)參數(shù)_1傳給a
	auto sub_fixed_b = bind(mul, _1, 200);
	cout << "3 * 200 = " << mul_fixed_a(3) << endl;
	return 0;
}

#include <iostream>
#include <functional>
using namespace std;
using namespace placeholders;
int sub(int a, int b)
{
    return a - b;
}
int main() {
    // 原函數(shù)是 a - b，重排后變成 b - a（_2 是新函數(shù)第2個(gè)參數(shù)，_1 是第1個(gè)）
    auto sub_swap = bind(sub, _2, _1);
    cout << "5 - 10 = " << sub_swap(10, 5) << endl; // 輸出：(5-10)*10=-50
    return 0;
}

#include <iostream>
#include <functional>
using namespace std;
using namespace placeholders;
class Calculator {
public:
    double multiply(double a, double b) {
        return a * b;
    }
};
int main() {
    Calculator calc;
    // 綁定 calc 作為 this 指針，_1 和 _2 是新函數(shù)的兩個(gè)參數(shù)
    auto calc_mul = bind(&Calculator::multiply, &calc, _1, _2);
    cout << "3 * 4 = " << calc_mul(3, 4) << endl; // 輸出：12
    return 0;
}

#include <stack>
#include <vector>
#include <string>
#include <functional>
#include <map>
using namespace std;
class Solution {
public:
    int evalRPN(vector<string>& tokens) {
        stack<int> st;
        // 用 map 存儲(chǔ)“操作符-function”映射
        map<string, function<int(int, int)>> op_map = {
            {"+", [](int a, int b) { return a + b; }},
            {"-", [](int a, int b) { return a - b; }},
            {"*", [](int a, int b) { return a * b; }},
            {"-", [](int a, int b) { return a - b; }},
            {"/", [](int a, int b) { return a / b; }},
            {"%", [](int a, int b) { return a % b; }}
        };
        for (auto& str : tokens) {
            if (op_map.count(str)) { // 匹配到操作符
                int right = st.top(); st.pop();
                int left = st.top(); st.pop();
                // 調(diào)用對(duì)應(yīng)的 function
                st.push(op_map[str](left, right));
            }
            else {
                st.push(stoi(str));
            }
        }
        return st.top();
    }
};

#include <functional>
#include <iostream>
using namespace std;
using namespace placeholders;
int main() {
    // 復(fù)利計(jì)算 lambda：rate=年利率，money=本金，year=年限，返回利息
    auto calc_interest = [](double rate, double money, int year) -> double {
        double ret = money;
        for (int i = 0; i < year; i++) {
            ret += ret * rate; // 每年復(fù)利
        }
        return ret - money; // 利息 = 最終金額 - 本金
    };
    // 用 bind 固定利率和年限，生成專(zhuān)用函數(shù)（只需傳入本金）
    function<double(double)> interest_3y_1_5 = bind(calc_interest, 0.015, _1, 3);  // 3年1.5%利率
    function<double(double)> interest_5y_2_0 = bind(calc_interest, 0.020, _1, 5);  // 5年2.0%利率
    function<double(double)> interest_10y_2_5 = bind(calc_interest, 0.025, _1, 10); // 10年2.5%利率
    // 調(diào)用簡(jiǎn)化版函數(shù)
    cout << "100萬(wàn) 3年1.5%利息：" << interest_3y_1_5(1000000) << endl; // 約45678.38
    cout << "100萬(wàn) 5年2.0%利息：" << interest_5y_2_0(1000000) << endl; // 約104080.80
    cout << "100萬(wàn) 10年2.5%利息：" << interest_10y_2_5(1000000) << endl; // 約280084.50
    return 0;
}

void print(int& x) { x++; cout << x << endl; }
int main() {
    int a = 10;
    auto func = bind(print, ref(a)); // 用 ref 綁定引用
    func(); // 輸出 11，a 被修改為 11
    return 0;
}