std :: tr1 :: function是否有一个合理的默认值？

Question

I spent some time googling but didn't really find anything. I want to be able to do this:

std::tr1::function<void()> foo(SOME_DEFAULT_FUNCTION_THAT_DOES_NOTHING);
//
//Some code that could possibly assign foo
//
foo();

Otherwise I have to do this:

std::tr1::function<void()> foo;
//
//Some code that could possibly assign foo
//
if(foo)
{
    foo();
}

I realize I could just make a function that does nothing, but I am looking for some standard way of not having to deal with checking to see if the function was given a value ala the null object pattern.

Answer 1

void noop() { }

Answer 2

Could you use a boost::optional<std::tr1::function<void()> > ? That way it allows it to be set or not, and you can use an if check to see if the function has been set.

Answer 3

在我的项目中，我使用

void noop(...) {}