The inline keyword doesn’t do what most people think it does. Especially true with every compiler upgrade or platform change. One worse engine once summarized its user cases as twofold: first, to hide visibility when linking, second, to judge the engineering org’s maturity.
That's exactly why I included it. People automatically think inlining is my intention. In reality I avoid templates and not all of my code is in a class. It's short enough to be a candidate for inlining so I put it in a header.