Implement Interface with Anonymous Class in C++
anonymous-class, c++, interface, java
Solution
what's wrong here?
For polymorphism to work, you need to pass the base class by reference (or pointer, if you prefer):
bool testIf(T t, Predicate<T> & predicate)
^
With that fixed, the code works for me, although it smells rather too much of Java for my taste.
are there other ways to do it?
In C++11 or later, a lambda would be more efficient, both in terms of performance, and noisiness of code. It removes the need to define and inherit from a base class, and to call a virtual function.
template <class T, class Predicate>
bool testIf(T t, Predicate predicate)
{
return predicate(t);
}
testIf(s, [](string const & s){return s.length() == 0;});
(Before C++11, you could do the same thing with a function object. It was slightly more verbose, but still gave shorter, more efficient code than the inheritance approach.)
Problem
In java we can implement an `interface` with Anonymous class like this : ``` import java.util.function.Predicate; public class Test { public static void main(String[] args) { System.out.println(testIf("", new Predicate<String>() { @Override public boolean test(String s) { return s.isEmpty(); } })); } public static <T> boolean testIf(T t, Predicate<T> predicate) { return predicate.test(t); } } ``` since Java 8 : ``` System.out.println(testIf("", String::isEmpty)); ``` how can we do it in c++? I wrote the following code but I'm getting compile error : ``` #include "stdafx.h" #include <iostream> #include <string> using namespace std; template <class T> class Predicate { public: virtual bool test(T) = 0; }; template <class T> bool testIf(T t, Predicate<T> predicate) { return predicate.test(t); } int main() { class : public Predicate <string> { public: virtual bool test(string s) { return s.length() == 0; } } p; string s = ""; cout << testIf(s, p); cin.get(); return 0; } ``` Error : no instance of function template "testIf" matches the argument list argument types are: (`std::string`, `class <unnamed>`) what's wrong here? are there other ways to do it? Thanks!