C++11 setting lambda in public function

Question

how to properly address this?

 class House{
 public:
  void startAction();
  void init(){
      startAction = [] () {}; 
  }  
 };

I have tried this, but it is said "Expression is not assignable"

I want to define the function of startAction, but inside the init method.

I do this because there's couple of variable in init method that i want to capture to pass to startAction.

why not capture the values in House? The values seemed to be owned by it, from your description — Dmitry Ledentsov
– Dmitry Ledentsov, Commented Jul 3, 2014 at 9:36
thanks, I really don't want to capture it in House, as i want to destroy it as init end. — Napitupulu Jon
– Napitupulu Jon, Commented Jul 3, 2014 at 9:45
@GulperEeL It doesn't really matter whether you store those values as members in the object or in the function's closure. The only difference is whether they're accessible from other member function sor not. — molbdnilo
– molbdnilo, Commented Jul 3, 2014 at 19:36

molbdnilo · Accepted Answer · 2014-07-03 09:41:31Z

6

You can't assign a value to a member function.

You could have a member variable that the member function calls, something like this:

class House{
 public:
  void startAction() { m_action(); }
  void init(){
      m_action = [] () {}; 
  }
 private:
  std::function<void()> m_action;  
};

But it's simpler to store the things you want to capture as members of House.

edited Jul 3, 2014 at 9:41

answered Jul 3, 2014 at 9:31

molbdnilo

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Comments

ALittleDiff · Accepted Answer · 2014-07-03 09:43:36Z

5

Try this:

class House {
  public:
    std::function<void ()> startAction;
    void init() {
        startAction = []() {};
    }  
};

int main() {
    House house;
    house.init();
    house.startAction();
    ...
}

edited Jul 3, 2014 at 9:43

answered Jul 3, 2014 at 9:36

ALittleDiff

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Comments

Dakorn · Accepted Answer · 2014-07-03 10:06:44Z

0

You can also instead of using std::function<void ()> use C style pointer to function. Look at the following code.

#include <iostream>

typedef void (*my_func)();

class House
{
public:
    my_func  m_ffunc;

    void init()
    {
        m_ffunc = [](){ std::cout << "Hello from m_ffunc" << std::endl;};
    }
};

int main()
{
    House myHouse;

    myHouse.init();
    myHouse.m_ffunc();

    return 0;
}

answered Jul 3, 2014 at 10:06

Dakorn

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1 Comment

MSalters Over a year ago

"there's couple of variable in init method that i want to capture". C-style pointers to function cannot capture variables. This doesn't answer the question.

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