Why can't my project find "function" in namespace std?

Question

I have the following code:

@interface Model ()
{
    //...
    std::function<bool(CGFloat, CGFloat)> greaterThan;
    std::function<bool(CGFloat, CGFloat)> lesserThan;

    //...
}
@end

Everything worked fine in my original project. I just created a new project, and dragged and dropped the files between the two, and in the new project I have the following errors for the above two lines:

No type named 'function' in namespace 'std'

I don't know what the problem is - The files are .mm , why can't it find function in the names space std ?

Answer 1

Add #include <functional> to the top of your code.

Also remember to use -std=c++0x (or equivalent) in your compiler parameters; this will enable C++11 standard which is required for std::function.