A ''cross-cutting concern'' is some software concern (synchronization, logging, memory allocation, NetworkTransparency, UI preferences) that is for the most part outside of (and orthogonal to) the ProblemDomain 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 UgLy.

Techniques include:

* TemplateMetaprogramming, augmented with PolicyObject''''''s (such as StandardTemplateLibrary allocators)
* MetaObjectProtocol''''''s, in particular things like before functions, after functions, etc.
* Decorators (both DecoratorPattern and the language feature in Java), delegation in general.
* TemplateMethodPattern (i.e. use of HookMethod''''''s)
* RPC tools
* Many of the CreationalPatterns can be used to allow variation of some cross-cutting concern at runtime.
* MultipleInheritance and MixIn''''''s
* ContextObject or ExplicitManagementOfImplicitContext

A programming paradigm dealing with this stuff is AspectOrientedProgramming.

A few ''bad'' techniques for dealing with CrossCuttingConcerns include:

* GrandCentralStation (aggregating lots of independent domain functionality into a BigBallOfMud just so the CrossCuttingConcern''''''(s) can be dealt with in one place).
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See also: VariationsTendTowardCartesianProduct
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CategoryComplexity, CategoryInfoPackaging CategoryAspectOrientation