bad_lambda.cpp

#include <iostream>
#include <unistd.h>

class bar{
public:
    bar(){}
    ~bar(){}
    void setLambda(std::function<void()> func){
        _func = func;
    }
    void onFinish(){
        _func();
    }
private:
    std::function<void()> _func;
};

class foo{
public:
    foo():
        a{3}
    {}
    ~foo(){}
    void setBadLambda(bar& bar){
        // bad idea! (*this) might be deleted when this lambda is called!
        bar.setLambda(
            [=](){
                std::cout << this->getA() << std::endl;
            }
        );
    }
    void setGoodLambda(bar& bar){
        // (*this) dosen't necessarily have to be alive!
        int var = this->getA();
        bar.setLambda(
            [var](){
                std::cout << var << std::endl;
            }
        );
    }
    int getA(){
        return a;
    }
    void setA(int arg){
        a = arg;
    }
private:
    int a;
};

int main(){
    bar _bar;

    foo* _foo = new foo;
    //_foo->setBadLambda(_bar);
    _foo->setGoodLambda(_bar);
    _foo->setA(3);
    delete _foo;
    foo* _hoge = new foo;
    _hoge->setA(2);

    sleep(1);

    _bar.onFinish();
    // prints 2 with badLambda, 3 with goodLambda

    delete _hoge;
    return 0;
}