std :: tr1 ::功能分配和绑定

Question

I'm trying to learn how to best use the std::function and the std::bind facilities in the standard library - I'm interested in the TR1 versions, as that's what I have available for now and I'm not aware of the differences, if any, between the TR1 implementations and the C++11 ones.

So for the sake of the exercise I've set up to construct a simple let's say "dispatcher". What I want is to be able to execute any function from the dispatcher based on some decisions taken later at runtime. I set up my class to have a general function data member like so:

class PoorDispatcher
{
 ...
 private:
     std::tr1::function<void()> m_f;
}

Then I assign to the data member the function I really want to call, similar to the below

...
m_f = std::tr1::bind(some_func, param1, param2, param3);
...
// then the call
m_f(); // SUCCESS

The above allows me to call successfully the function I want but I'm not sure it's the right thing to do. The questions:

1. Is the above usage scenario "sane"? Are there any better alternatives?
2. The above method poses a problem when trying to bind to a function which returns something. How can I retrieve the return value? (In my silliness I tired to cast the function objects without much success)

Answer 1

The template argument to std::function is the actual function type. void() means a function which takes no arguments and returns no value.

If you want to store a function that returns a value you have to create a new function object. Or if you are not sure if the function will return something, use boost.optional .