More than one invariant per struct/class

[Pelle]

On Thu, 04 Aug 2011 11:32:03 +0200, simendsjo <simendsjo at gmail.com> wrote:

> I would like to use a template mixin to add some fields to a struct, but  
> I'd also like the template to add additional invariant checks without  
> having to remember to add this for all struct/classes that mixes in this  
> code.
>
> class C {
>      int a;
> }
>
> mixin template EmbedC() {
>      C _c;
>
>      // oops.. more than one invariant
>      invariant() {
>          assert(_c);
>      }
>
>      void close() {
>          _c = null;
>      }
> }
>
> struct S {
>      int i = 10;
>      invariant() {
>          assert(i >= 10);
>      }
>
>      mixin EmbedC!();
> }
>
> void main() {
>      S s;
>      s.close();
>      s._c.a = 10; // access violation, but I want assertion from  
> invariant
> }

What happens if you replace assert(_c) with assert(_c !is null)?