 the
      C++ type system; for example, is a type a pointer or a reference type? Or does
      a type have a trivial constructor, or a const-qualifier? The type-traits classes
      share a unified design: each class inherits from the type <a class="link" href="reference/integral_constant.html" title="integral_constant">true_type</a>
      if the type has the specified property and inherits from <a class="link" href="reference/integral_constant.html" title="integral_constant">false_type</a>
      otherwise