x-macro

X macros are an idiomatic usage of programming language macros for generating list-like structures of data or code. They are most useful when at least some of the lists cannot be composed by indexing, such as compile time. They provide reliable maintenance of parallel lists whose corresponding items must be declared or executed in the same order.
Examples of such lists particularly include initialization of arrays, in concert with declarations of enumeration constants and function prototypes; generation of statement sequences and switch arms; etc.
Usage of X macros dates back to the 1960s. It remains useful in modern-day C and C++ programming languages, but remains relatively unknown.

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