Simple example of std::move use with stacks to avoid copies.

gistfile1.cpp

#include <stack>
#include <memory>

int main() {
  std::stack<std::unique_ptr<int>> A, B;

  A.push(std::unique_ptr<int>(new int{1}));
  A.push(std::unique_ptr<int>(new int{2}));
  A.push(std::unique_ptr<int>(new int{3}));

  // Can't do this -- unique_ptrs aren't copyable.
  /*
  B.push(A.top());
  A.pop();
  */

  // Can do this.
  B.push(std::move(A.top()));
  // Now A.top() is in a safe-to-destruct but unspecified state.
  // for a unique_ptr that means null. So be careful if that violates
  // another object's invariant!
  B.pop();
}