When should I use -inl.h files?

Question

I just noted this item in the Google C++ Coding Style Guide - and I don\'t quite get it.

If I put an inline method or function in a file other than the header included b

Answer 1

According to latest Google coding style, it is no longer allowed https://google.github.io/styleguide/cppguide.html#Variable_Names

Prefer placing the definitions for template and inline functions in the same file as their declarations. The definitions of these constructs must be included into every .cc file that uses them, or the program may fail to link in some build configurations. If declarations and definitions are in different files, including the former should transitively include the latter. Do not move these definitions to separately included header files (-inl.h); this practice was common in the past, but is no longer allowed.