https://issues.dlang.org/show_bug.cgi?id=23729 --- Comment #8 from ryuukk_ <ryuukk.dev at gmail.com> --- The format function is used in a mixin context, therefore it's compile time https://github.com/dlang/dmd/blob/d344030e01688fbe99b82438f4dae8dfa3f6aee3/druntime/src/core/internal/atomic.d#L90 --