http://d.puremagic.com/issues/show_bug.cgi?id=3578

           Summary: Impossible to run a struct invariant using assert(s)
           Product: D
           Version: 1.041
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: llucax@gmail.com


--- Comment #0 from Leandro Lucarella <llucax@gmail.com> 2009-12-05 08:24:54 PST ---
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).

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Leandro Lucarella <llucax@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #1 from Leandro Lucarella <llucax@gmail.com> 2010-06-21 17:44:13 PDT ---
*** Issue 4326 has been marked as a duplicate of this issue. ***

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Shin Fujishiro <rsinfu@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rsinfu@gmail.com


--- Comment #2 from Shin Fujishiro <rsinfu@gmail.com> 2010-10-16 12:02:06 PDT ---
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.

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--- Comment #3 from Leandro Lucarella <llucax@gmail.com> 2010-10-16 16:06:59 PDT ---
(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.

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--- Comment #4 from github-bugzilla@puremagic.com 2012-01-23 01:50:33 PST ---
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)

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED


--- Comment #4 from github-bugzilla@puremagic.com 2012-01-23 01:50:33 PST ---
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)

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