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Not related to the standardisation of C++, but another trick is to keep
track of which pages of memory are read-only, and to not bother copying the
string if it's in read-only memory. Of course this will only work properly
if your program doesn't change the permissions on pages of memory.

When I program microcontrollers I just check if the string address is less
than 0x20000, and then I know it's in Flash rather than RAM. No need to
copy it if it's in the read-only Flash.