Some types, such as types with @disabled copy constructors and types with opAssign overloads that accept the rhs only by ref, satisfy one but not the other. It would be useful for generic code to be able to distinguish these types from types that do not allow assignment at all.
@pbackus created dlang/phobos pull request #7626 "Fix issue 21237: isLvalueAssignable and isRvalueAssignable should be …" fixing this issue: - Fix issue 21237: isLvalueAssignable and isRvalueAssignable should be public https://github.com/dlang/phobos/pull/7626
dlang/phobos pull request #7626 "Fix issue 21237: isLvalueAssignable and isRvalueAssignable should be …" was merged into master: - 7ae3e7126c2312454235c895965db34aee9f7a06 by Paul Backus: Fix issue 21237: isLvalueAssignable and isRvalueAssignable should be public https://github.com/dlang/phobos/pull/7626