https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116399
--- Comment #13 from 康桓瑋 <hewillk at gmail dot com> --- (In reply to Jonathan Wakely from comment #12) > Implementation-defined means the implementation must define it (and document > it). > > If the implementation says the types are different, then they're different, > and it's not a common range. I found that in the original paper, the implementation experience of alias_view was designed to be sized_range, but the implementation of libstdc++ was not. I'm not sure it's reasonable or trivial for alias_view to be sized_range, the standard does not specify it, perhaps we should explicitly say so just like common_range. If it's trivial to make it satisfy sized_range, then perhaps we should submit to the LWG to require it.
