C++11: =default

Instead of providing a body for a class constructors or assignment operators, you can specify =default in the declaration. Here is an example:

#include <iostream>
class A
{
 public:
  A() = default; // Without this line, this file will not compile.
  A(const A& a)      {std::cout << "Copy CTOR called; ";}
  A& operator=(A& a)
  {
    std::cout << "Assignment Operator called; ";
    return *this;
  }
};
int main()
{
  A a1;
  A a2(a1); // Copy CTOR called
  a1 = a2;  // Assignment Operator called
  return 0;
}
// Output: Copy CTOR called; Assignment Operator called;

Reference: https://isocpp.org/wiki/faq/cpp11-language-classes#default-delete