How does D improve design practices over C++?

[Tony]

"Janderson" <ask at me.com> wrote in message 
news:gf0e9n$31ff$1 at digitalmars.com...
> Tony wrote:
>
>>> long square_root(long x)
>>>     in
>>>     {
>>>     assert(x >= 0);
>>>     }
>>>     out (result)
>>>     {
>>>     assert((result * result) <= x && (result+1) * (result+1) >= x);
>>>     }
>>>     body
>>>     {
>>>     return cast(long)std.math.sqrt(cast(real)x);
>>>     }
>>
>> Or if one wanted something like that in C++:
>>
>> class MyInvariant
>> {
>>     MyInvariant(long& x)
>>     {
>>         // do a check on entry
>>     }
>>
>>     ~MyInvariant()
>>     {
>>         // do a check on exit
>>     }
>> };
>>
>
> You should know that the syntax I presented above is not an invariant in D 
> (that's a contractual check).  An invariant check in D looks like this:
>
> class Foo
> {
>     public void f() { }
>     private void g() { }
>
>     invariant()
>     {
> //Checked for both f and g
>     }
> }
>
> The invariant example was what I originally said in my first reply was a 
> lot of extra work in C++.  Note I used invariant checks a lot in C++ and 
> D's invariant checks are far better.  You might want to read though the D 
> documentation so that what I've said makes more sense.  You seem to reply 
> only half reading what I've said (case-in-point above).
>
> The documentation can be found here:
>
> http://www.digitalmars.com/d/2.0/lex.html
>
> and here for 1.0
>
> http://www.digitalmars.com/d/1.0/lex.html

I need a large list of examples where invariants were used because I just 
don't see many opportunities to use them in my own codebase. Also, they seem 
mainly useful as a development aid rather than as production code (similar 
to turning off assertions in release code).

Tony