Argument Dependent Lookup (ADL)

C++ uses the arguments and the namespace of arguments to look up a function.

This is called Argument Dependent Lookup (ADL), and is also known as Koening's lookup. This process is sometimes reponsible for strange compile errors.

Reference: http://en.wikipedia.org/wiki/Argument_dependent_name_lookup


Here is a short video on an application of ADL:
Video: Using ADL to Stream Out Objects