The Boost Metaprogramming Library (MPL) is a library which defines tools for metaprogramming in CeePlusPlus.  It is one of the BoostLibraries.  It is widely used in other boost libraries including BoostFusion. Its use is often combined with use of BoostTypeTraits.

The book CppTemplateMetaprogramming gives an introduction to its use.
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CategoryBoost CategoryCpp CategoryCppTemplates CategoryMetaprogramming