This is exactly right, and the "Man-or-Boy" benchmark hits the worst-case scenario for libstdc++ specifically. The optimization fails here. My "copy-by-value" comment refers to the ownership semantics. Since std::function owns its storage, and the Man-or-Boy recursion passes the closure into the next layer (often by value or by capturing it into a new closure), we trigger the copy constructor. If the SBO limit is exceeded, that copy constructor performs a new heap allocation and a deep copy of the state.