15.lambda表达式

#include <iostream>
#include <array>
using namespace std;

//解决函数怀孕现象
//[](){}
//[] =引用,只读 =mutable读原本改副本 &读写原本 //&a,b a可读写,b只能读
//() 参数,int a,int b
//{}语句
void main()
{
    //lambda表达式
    auto fun1 = [] {cout << "hello" << endl; cout << "hello2" << endl; };//函数指针
    fun1();//括号起到调用的作用

    //[](参数列表){执行逻辑}
    auto fun2 = [](char *str) {cout << str << endl; };
    fun2("hello3");

    //lambda带参函数
    auto fun3 = [](int a, int b) {return a + b; };
    cout << fun3(10, 19) << endl;

    //->用在(){}之间,用于确定返回值类型
    auto fun4 = [](int a, int b)->double {return a + b; };
    cout << fun4(10, 19) << endl;

    //decltype解决类型自动推理
    auto fun5 = [](int a, int b)->decltype(a+b) {return a + b; };
    cout << fun5(10, 19) << endl;

    int num1 = 20;
    int num2 = 33;
    //=可以使用外部变量,只能读不能写
    auto fun6 = [=](){cout << num1 << num2 << endl; };
    fun6();

    //&可以使用外部变量,读写(对原数据的操作)
    auto fun7 = [&](){num1 = 1; cout << num1 << num2 << endl; };
    fun7();

    //mutable可以使用外部变量,读写(副本机制,不对原数据进行改变)
    auto fun8 = [=]()mutable{num1 = 1; cout << num1 << num2 << endl; };
    fun8();

    //指定可读写的元素 num1可读可写,num2只能读
    auto fun9 = [&num1, num2]() {num1 = 30; cout << num2 << endl; };
    fun9();

    //mutable可读可写但作用的是副本
    auto fun10 = [num1, num2]() mutable{num1 = 30; cout << num2 << endl; };
    fun10();

    //lambda与auto
    auto fun11 = [](auto a, auto b)->decltype(a+b){return a + b; };
    cout << fun11(1,3.9) << endl;

    //内嵌调用lambda
    array<int, 10> myarray{1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
    for_each(myarray.begin(), myarray.end(), [](int &num) {num += 1; cout << num << endl; });
    cin.get();
}