For example, I have the following Java code:
public class Main {
public static void main(String[] args) {
System.out.println(maker(Employee::new));
}
private static Employee maker(Supplier<Employee> fx) {
return fx.get();
}
}
class Employee {
@Override
public String toString() {
return "A EMPLOYEE";
}
}
What will be the C++ equivalent?
Supplier is a function taking no arguments and returning some type: you can represent that with std::function:
#include <iostream>
#include <functional>
#include <memory>
// the class Employee with a "print" operator
class Employee
{
friend std::ostream& operator<<(std::ostream& os, const Employee& e);
};
std::ostream& operator<<(std::ostream& os, const Employee& e)
{
os << "A EMPLOYEE";
return os;
}
// maker take the supplier as argument through std::function
Employee maker(std::function<Employee(void)> fx)
{
return fx();
}
// usage
int main()
{
std::cout << maker(
[]() { return Employee(); }
// I use a lambda here, I could have used function, functor, method...
);
return 0;
}
I didn't use pointers here nor the operator new to allocate Employee: if you want to use it, you should consider managed pointers like std::unique_ptr:
std::unique_ptr<Employee> maker(std::function<std::unique_ptr<Employee>(void)> fx)
{
return fx();
}
// ...
maker(
[]()
{
return std::make_unique<Employee>();
}
);
Note: the call to operator<< should then be modified because maker will return a pointer instead of an object.
You can use C++ template class to achieve the goal:
template<typename TR> class Supplier
{
private:
TR (*calcFuncPtr)();
public:
Supplier(TR(*F)())
{
calcFuncPtr = F;
}
TR get() const
{
return calcFuncPtr();
}
};
Usage sample:
#include <string>
#include <iostream>
struct Employee
{
public:
std::string ToString()
{
return "A EMPLOYEE";
}
};
Employee maker(const Supplier<Employee>& fx)
{
return fx.get();
}
Employee GetInstanceFunc()
{
return Employee();
}
int _tmain(int argc, _TCHAR* argv[])
{
Employee employee(maker(GetInstanceFunc));
std::cout << employee.ToString();
return 0;
}
Implicit type conversion at line maker(GetInstanceFunc) allows to use Supplier class without explicit template instantiation.
