By Patrick Celedio
A helper function is a function with a certain functionality that will be reused frequently, usually self-defined by the same writer of the corresponding C++ class. It is seen as part of the userful interface of a class and is recommended to be part of the same namespace as the class in order to establish a clear relationship of the class and helper functions, and allows them to be found by argument dependent lookup.
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What are helper functions in C++?
C.5: Place helper functions in the same namespace as the class they support