Broken contract programing

[Timon Gehr via Digitalmars-d]

On 05/13/2015 02:16 PM, Benjamin Thaut wrote:
> On Wednesday, 13 May 2015 at 12:05:48 UTC, Timon Gehr wrote:
>> On 05/13/2015 12:51 PM, iackhtak wrote:
>>> There was discussion about broken contract programing. One broken
>>> thing was "in" contract within inheritance. If you add different
>>> "in"-contract in overridden parent and derived function only one
>>> will be checked.
>>
>> No, this is incorrect. Only one needs to pass and if one does not, the
>> other is checked as well.
>>
>
> Wasn't the point that the set of values the derived contract accepts
> must be  a superset of the set of values the base contract accepts?

Yes, but this is enforced automatically.

> E.g.
>
> class Base
> {
>     int foo(int x)
>     in { assert( x >= 0; );
>     body { ... }
> }
>
> This would be ok:
>
> class DerivedOk : Base
> {
>     override int foo(int x)
>     in { assert( x >= 0 || x < -5 ); }
>     body { ... }
> }
>
> This would be broken:
>
> class DerivedBroken : Base
> {
>     override int foo(int x)
>     in { assert( x >= 0 && x < 5 ); }
>     body { ... }
> }
> ...

This will accept the same arguments as Base. Only one in-contract in the 
inheritance chain must pass in order for the call to go through.