Ruby

1.instance_eval do @a = 1 end 

There's a missing check at the top of vm_setivar_fastpath, should be:

 if (UNLIKELY(RB_SPECIAL_CONST_P(obj))) { // example code: 1.instance_eval { @a = 1 } rb_check_frozen(obj); // raise FrozenError, because it's always frozen return Qundef; }