It's not that defer is slow in absolute terms†; it's that it's slower than it needs to be for no good reason. The corresponding C++ feature (RAII) is "free" (as

It's not that defer is slow in absolute terms†; it's that it's slower than it needs to be for no good reason. The corresponding C++ feature (RAII) is "free" (as in, it adds no overhead over manually writing the cleanup code), while defer is not. Defer would be easier to use for the programmer, easier for the compiler writer, and faster at runtime if it were block-scoped. †Though the linked list that the compiler has to generate could hit malloc, which costs more than a few nanoseconds.