Analysis of a library development technique that allows users to decide whether or not to consume the library as "header-only".

opt-in header-only libraries

    by Vittorio Romeo

From the article:

Libraries can be designed and implemented in order to allow users to choose between header-only usage, static linking or dynamic linking. [...] The main idea is to conditionally include .cpp files depending on a preprocessor macro, which can be defined during compilation. Functions also have to be conditionally decorated with the inline specifier.