`std::source_location` does not have to be a function argument. It can also be used in an NSDMI, in which case it ends up being instantiated whenever the NSDMI

`std::source_location` does not have to be a function argument. It can also be used in an NSDMI, in which case it ends up being instantiated whenever the NSDMI is used, i.e. at every aggregate initialization site. https://godbolt.org/z/v5rhjqdbY https://godbolt.org/z/v5rhjqdbY Of course, that doesn't really allow you to do anything that you couldn't already do in the with a constexpr function (see below). In particular, such a struct can be used as a non-type template parameter, but a `template<NSDMI sloc = NSDMI{}> void foo();` will merely report the line where the template is defined, not where `foo` is called. // Results in a compile-time constant, so can be used everywhere where __LINE__ could be used. constexpr int line(std::source_location loc = std::source_location::current()) { return loc.line(); } So std::source_location can fully replace __FILE__/__LINE__, but it cannot always replace the macro where __FILE__/__LINE__ were being used.