#include <iostream>
#include <vector>
#include <algorithm>
// lambda practice

int main() {
   // [] 为存储需要的外部变量， 可分为值获传入与地址传入
   // （）函数中的参数列表
   // { } 函数体

	auto square = [](int x) {return x * x; };
	auto is_even = [](int x) {return x % 2 == 0; };

	std::cout << "square =  " << square(10) << std::endl;
	std::cout << "is_even =  " << is_even(10) << std::endl;;

	int th = 10;
	auto bigger = [th](int x) { return x > th; };
	auto inc = [&th]() {th++; };
	inc();
	std::cout << "bigger = " << bigger(20) << std::endl;
	std::cout << "inc th = " << th << std::endl;

	int seed = 0;
	auto gen = [seed]() mutable {return ++seed; };
	std::cout << "gen seed = " << gen() << std::endl;
	std::cout << " seed = " << seed << std::endl;
	/*
	* mutable: 对类、结构体中的非静态成员变量有效。
	* 作用： 允许某个成员变量在const成员函数中也可以被修改
	*/

	auto add = [](auto a, auto b) { return a + b; };
	std::cout << "add float = " << add(1.0, 6.3) << std::endl;
	std::cout << "add int = " << add(1, 7) << std::endl;

	//  -> double 明确返回值类型
	auto safe_div = [](double a, double b) -> double {
		return (b == 0) ? 0.0 : (a / b);
	};
	std::cout << "safe_div = " << safe_div(1, 0) << std::endl;
	std::cout << "safe_div = " << safe_div(1, 2) << std::endl;


	std::vector v = {6, 2, 4, 7, 0, 55, 89, 34};
	std::sort(v.begin(), v.end(), [](const auto& a, const auto& b) {return a < b; });
	for(const auto& p:v)
		std::cout << p << std::endl;

	//transform 按照某种规则映射
	std::transform(v.begin(), v.end(), v.begin(), [](int x) {return x * 2; });
	for (const auto& p : v)
		std::cout << p << std::endl;

}