Bug 6912 – const(T)[] can be implicitly cast to inout(const(T)[])

Consider: int[] y; inout(const(int)[]) foo(inout(int) x){ y=new int[10]; const(int)[] q = y; inout a = q; return a; } void main(){ immutable int x; immutable int[] oops = foo(x); assert(is(typeof(oops[0]) == immutable)); auto oldoops_0 = oops[0]; y[0]++; assert(oops[0] != oldoops_0); } This is caused by the fact that !is(inout(const(int)[])==inout(int[])), i.e. inout is currently non-transitive in certain cases and making it 'override' const transitively will fix the issue.

inout a = q; This line should fail to compile. const does not implicitly cast to inout. Note that: immutable a = q; doesn't work. inout should follow the same restrictions. I don't think this has to do with transitivity (and indeed, inout cannot override const or immutable). It's just a simple case of inout cannot be implicitly cast from something else. Remember, inout can get implicitly cast back to immutable or mutable upon function return. I don't think inout should override *any* qualifiers without casts.

(In reply to comment #1) > inout a = q; > > This line should fail to compile. const does not implicitly cast to inout. > Yes, but the issue here is that it casts to inout(const(int)[]). (dmd rejects casting const(int[]) to inout(int[]) for exampe) > Note that: > > immutable a = q; > > doesn't work. inout should follow the same restrictions. > > I don't think this has to do with transitivity (and indeed, inout cannot > override const or immutable). It's just a simple case of inout cannot be > implicitly cast from something else. > > Remember, inout can get implicitly cast back to immutable or mutable upon > function return. I don't think inout should override *any* qualifiers without > casts. You are right, it is not a transitivity/overriding issue. Currently inout(const(T)) == inout(immutable(T)) == inout(T). That is bad, for example, how to represent the element type of inout(const(char)[]) ? (DMD treats it as const(char), which is obviously wrong, it should be inout(const(char)).)

https://github.com/D-Programming-Language/dmd/pull/504 This patch will forbid some conversions like follows. e.g. const(int)[] to inout(const(int)[]) const(int)[int] to inout(const(int)[int]).

I think this should be accepts-invalid, since the given example code should not compile.

(In reply to comment #4) > I think this should be accepts-invalid, since the given example code should not > compile. Wow, I'm sorry, and thank you for your fix.

(In reply to comment #5) > (In reply to comment #4) > > I think this should be accepts-invalid, since the given example code should not > > compile. > > Wow, I'm sorry, and thank you for your fix. Don't worry about it! The main fix is the patch, my change was a nitpick :)