C++ : Pass Dynamic Functions and Store Functions?

Question

I have two questions regarding functions in C++: can you dynamically declare a function when passing it as a reference, and is it possible to store functions to use later?

Passing Dynamic Function?

My question may not be worded perfectly clear, but what I mean is in Java you quite often see code that looks like:

button.addActionListener( new ActionListener( ) { public void actionPerformed( ActionEvent e ) { System.out.println( "..." ); } } );

or JavaScript:

$( ".class" ).each( function( ) { alert( "..." ); } );

While in C++ you are limited to:

void print( ) { std::cout << "..." << std::endl; } void func( void ( &f )( ) ) { f( ); } // ... func( print );

and can not do something like

void func( void ( &f )( ) ) { f( ); } // ... func( void f( ){ ... } );

Is this just a limitation to C++?

Storing Functions?

Is it at all possible to store similar functions into a container to be called later? An example of the idea (which does not work) is:

std::vector< void( ) > storage; void callMeLater( void ( &f )( ) ) { storage.push_back( f ); } void popFunction( ) { void f( ) = storage.pop_back( ); f( ); }

These ideas both came to me when working on an Event system, to see if my Timer object could also handle delayed functions as well as event calls. As I have never seen these used in any C++ code, I doubt they are possible but would love to be shown otherwise!

Thank you.

Sebastian Mach · Accepted Answer · 2012-02-15 16:40:24Z

With the current standard, it has become very easy:

#include <functional> void foo (std::function<float(float,float)> bar) { std::cout << bar (0.5, 0.75); std::function<float(float,float)> frob = bar; }

Within the angle brackets you declare the output (a single float in this case) and input (two floats).

You could then call it like this:

float perlin_noise_function (float x, float z) { ... } class PerlinNoiseFunctor : public std::binary_function<float(float,float)> {...}; int main () { // pass function pointer foo (perlin_noise); // pass functor PerlinNoiseFunctor pnf; foo (pnf); // pass lambda function foo ([] (float x, float z) { ... }); }

You could also replace foo like this:

template <typename F> void foo (F f) ;

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