Bug 3578 – Impossible to run a struct invariant using assert(s)

This fails to compile (with -unittest): --- struct S { invariant() { assert (false); } unittest { S s; assert (s); } } --- With this error message: inv.d(3): Error: expression s of type S does not have a boolean value With both DMD 1 and 2 (tested with DMD 1.041 and DMD 2.037. Changing struct to class compiles fine (and dumps a core if you run it, of course ;). Thes specs are not clear on this in both D1 and D2. Invariant is only mentioned in structs, but I guess it's more likely to think that the description of class invariant apply to structs too, so I guess this should be supported in both D1 and D2. If it's a change to big to make it in D1, I think the specs should be updated to clarify the differences between struct and class invariants. In D2 I don't see why the language should not be updated to support this, since there is no other way to trigger an invariant check (and, for example, invariant is not executed when a struct is constructed or when using alias this, I think).

*** Issue 4326 has been marked as a duplicate of this issue. ***

It's undocumented, but struct invariants are fired on pointers: -------------------- struct S { invariant() { assert(0); } // (3) } void main() { S s; assert(&s); } -------------------- % dmd -run test.d core.exception.AssertError@test(3): Assertion failure -------------------- Though it's non-intuitive, I find it reasonable considering that structs can define opCast to bool. assert(s) would be ambiguous if s had both invariant and opCast!bool.

(In reply to comment #2) > It's undocumented, but struct invariants are fired on pointers: > -------------------- > struct S > { > invariant() { assert(0); } // (3) > } > void main() > { > S s; > assert(&s); > } > -------------------- > % dmd -run test.d > core.exception.AssertError@test(3): Assertion failure > -------------------- > > Though it's non-intuitive, I find it reasonable considering that structs can > define opCast to bool. assert(s) would be ambiguous if s had both invariant > and opCast!bool. I never expected that, but it makes sense as you mention. I guess this behavior should be documented in the specs.

Commit pushed to https://github.com/D-Programming-Language/d-programming-language.org https://github.com/D-Programming-Language/d-programming-language.org/commit/8ed7c3ded95c50a4dc297a272fa53c0deb18e68e fix Issue 3578 - Impossible to run a struct invariant using assert(s)