When the effect of cv-qualification on layout compatibility was previously discussed (see issue 1334), the question was resolved by reference to the historical origin of layout compatibility: it was a weakening of type correctness that was added for C compatibility, mimicking exactly the corresponding C specification of compatible types in this context and going no further. Because cv-qualified and cv-unqualified types are not compatible in C, they were not made layout-compatible in C++.

Because of specific use-cases involving std::pair and the like, however, and in consideration of the fact that cv-qualified and cv-unqualified versions of types are aliasable by the rules of 7.2.1 [basic.lval], the outcome of that question is worthy of reconsideration.