Koenig Lookup

Argument-Dependent Lookup (ADL)

ADL defines rules lookup for an unqualified function names.

Example Use Case

namespace nsp
{
   class TestClass
   {
   };

   void PrintTestClass(const TestClass&)
   {
   }
}

int main()
{
    nsp::TestClass a;

    // Qualifying PrintTestClass with namespace is not needed
    // e.g. nsp::PrintTestClass(a);
    PrintTestClass(a);

    return 0;
}

Special Use Cases

C++ Core Guidelines: Surprises with Argument-Dependent Lookup mentions interesting cases with ADL.

References