Bug 22290 – Disallow assignment to a non-elaborate field of an rvalue

struct S{ int i; } S _s; S s(){ return _s; //returns DUPLICATE of _s, not _s by reference } void main(){ s().i = 42; //new user might think _s.i is the variable that gets modified. assert(!(_s.i == 42)); //They would be wrong. } Yes, there are valid cases when the rvalue DOES need to be mutated. However, in cases like these, there are no side-effects, and the computation becomes completely redundant, and the user finds out their error at runtime with no proper diagnostic, since the program even successfully executes, not just compiles.

*** This issue has been marked as a duplicate of issue 11920 ***