Exceptional C++: 47 Engineering Puzzles, Programming Problems, and Solutions

Chapter 31. Name Lookup and the Interface Principle—Part 1

Difficulty: 9½

When you call a function, which function do you call? The answer is determined by name lookup, but you're almost certain to find some of the details surprising.

In the following code, which functions are called? Why? Analyze the implications.

namespace A 
{
  struct X;
  struct Y;
  void f( int );
  void g( X );
}

namespace B
{
  void f( int i )
  {
    f( i );   // which f()?
  }
  void g( A::X x )
  {
    g( x );   // which g()?
  }
  void h( A::Y y )
  {
    h( y );   // which h()?
  }
}

Solution

Two of the three cases are (fairly) obvious, but the third requires a good knowledge of C++'s name lookup rules—in particular, ...