I'd heard people mention porting problems from HP-UX with code written with the assumption of writable strings. More a compiler than OS thing anywhere, nothing stops a compiler from putting it in one kind of segment or another. Some let you choose whether strings are writable. You can reference a non-object, like a structure, union, or atomic type.

But it's still a pointer and should be checked, but a hidden pointer that acts like a real variable. A pointer you can and should check if it's NULL before you use it, but a reference, you have to take the pointer of it to check, and people frequently don't bother.