c++ convert class to boolean

Question

With all of the fundamental types of C++, one can simply query:

if(varname)

and the type is converted to a boolean for evaluation. Is there

Answer 1

The C++11 approach is:

struct Testable
  {
    explicit operator bool() const
      { return false; }
  };

int main ()
  {
    Testable a, b;
    if (a)      { /* do something  */ }  // this is correct
    if (a == b) { /* do something  */ }  // compiler error
  }

Note the explicit keyword which prevents the compiler from converting implicitly.