https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66699
--- Comment #4 from Martin Sebor <msebor at gcc dot gnu.org> --- Being described as similar doesn't imply they are identical in every detail. std::pair and std::tuple are distinct classes with different requirements on each. If you believe the are required to behave identically in this respect (i.e., have their subobjects defined in the same order) you need to point to the specific wording that guarantees it.
