A cross-cutting concern is some software concern (synchronization, logging, memory allocation, Network Transparency, UI preferences) that is for the most part outside of (and orthogonal to) the Problem Domain a software component/module is concerned with, but important nonetheless. Many different techniques have been developed to deal with these--some good, some bad, some Ug Ly.
Techniques include:
Template Metaprogramming, augmented with Policy Objects (such as Standard Template Library allocators)
Meta Object Protocols, in particular things like before functions, after functions, etc.
Decorators (both Decorator Pattern and the language feature in Java), delegation in general.
Template Method Pattern (i.e. use of Hook Methods)
RPC tools
Many of the Creational Patterns can be used to allow variation of some cross-cutting concern at runtime.
A programming paradigm dealing with this stuff is Aspect Oriented Programming.
A few bad techniques for dealing with Cross Cutting Concerns include:
Grand Central Station (aggregating lots of independent domain functionality into a Big Ball Of Mud just so the Cross Cutting Concern(s) can be dealt with in one place).
See also: Variations Tend Toward Cartesian Product
See original on c2.com 