#include <functional>
#include <iostream>
 
void sampleFunction()
{
    std::cout << "This is the sample function!\n";
}
 
void checkFunc(std::function<void()> const& func)
{
    // Use operator bool to determine if callable target is available.
    if (func)  
    {
        std::cout << "Function is not empty! Calling function.\n";
        func();
    }
    else
        std::cout << "Function is empty. Nothing to do.\n";
}
 
int main()
{
    std::function<void()> f1 = []{};
    std::function<void()> f2(sampleFunction);
 
    std::cout << "f1: ";
    checkFunc(f1);
 
    std::cout << "f2: ";
    checkFunc(f2);
}

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