Also, while it's easier to just include another header file, it can have a pretty serious impact on build times. If you compare the same program with header-only libraries to one with libraries using the normal header declaration/source definition split, it's much faster. I never worried about this too much in C, but C++ takes long enough to build as it is.

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As a sidenote, I remember my brain hurting when I learned about C++ just redefining `inline`. It would have made much more sense to just define a new keyword.

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