From: nobu@... Date: 2020-04-02T13:33:36+00:00 Subject: [ruby-core:97674] [Ruby master Misc#16750] Change typedef of VALUE for better type checking Issue #16750 has been updated by nobu (Nobuyoshi Nakada). Assignee set to joke No tags in Redmine now. ---------------------------------------- Misc #16750: Change typedef of VALUE for better type checking https://bugs.ruby-lang.org/issues/16750#change-84879 * Author: Dan0042 (Daniel DeLorme) * Status: Open * Priority: Normal * Assignee: joke ---------------------------------------- VALUE is currently defined as `typedef unsigned long VALUE`, but as we all know that only creates an _alias_, not an actual _type_. Since the compiler gives no warnings when comparing with other integer values, it's easy to have bugs such as `v == 42` which should have been `v == INT2FIX(42)`. Actually not so long ago I saw nobu fixing a bug of that kind where an ID had been mixed up with a VALUE. So in order to prevent these kinds of bugs I propose changing VALUE to a non-scalar type such as: ```c //example for 64-bit system typedef union VALUE { struct RBasic* as_basic; //easy access to obj.as_basic->klass and obj.as_basic->flags void* as_ptr; //can assign ptr = obj.as_ptr without a cast unsigned long i; //raw int value for bitwise operations int immediate : 3; //obj.immediate != 0 if obj is immediate type such as fixnum, flonum, static symbol int is_fixnum : 1; //obj.is_fixnum == 1 if obj is fixnum struct { int flag : 2; //obj.flonum.flag == 2 if obj is flonum int bits : 62; } flonum; struct { int flag : 8; //obj.symbol.flag == 0x0c if obj is a static symbol int id : 56; //-> obj.symbol.id == STATIC_SYM2ID(obj) } symbol; } VALUE; ``` This will allow proper type-checking via the compiler. A little-known fact, structs and unions can be passed (and returned) by value to functions; this 64-bit union has the same performance as a 64-bit int. This approach also allows to simplify code like `((struct RBasic*)obj)->flags` into the much more readable `obj.as_basic->flags`, and `FIXNUM_P(obj)` can be expressed directly as `obj.is_fixnum`. The only downside is that direct comparison of union variables is not possible, so you would need to use for example `obj.i == Qfalse.i` To summarize, stricter type-checking would eliminate an entire class of bugs, and I estimate this change would require modifications to **no more than 14%** of the codebase (62,213 lines). Very much worth it I believe. -- https://bugs.ruby-lang.org/ Unsubscribe: