On Thu, 15 Jun 2000 22:11:34 -0400, Andrew Hunt <andy / Toolshed.Com>
wrote:
>
>    >And if you were to ask an Eiffel adherent, most would reply that
>    >" programming by contract" includes static typing. Indeed what is
>    >meant by contract? According to OOSE the contract is the interface
>    >and the constrictions on the interface ( pre and postconditions,
>    >invariants ). This definition implies that a contract requires static
>    >typing.
>
>I disagree strongly.  While Meyer is an advocate of static typing, I
>see no reason that DBC cannot be effective in a dynamically typed
>environment -- in fact, it seems to me that DBC could be even *more*
>useful in a dynamic environment than in a static one.
>
>A precondition asserts a routine's expectations of the state of the
>world.  A poscondition verifies the results of the operation.  
>Why do you feel that static typing has *anything* to do with expressing
>the semantics of an operation in this manner?  I would argue that
>DBC in a dynamic language gives you the best of both worlds -- some
>guarantee that you're doing the right thing (the objects you are
>dealing with honor the semantics you expect, regardless of type), 
>along with the flexibility of dynamic types.

The reason I say that static typing is a part of DBC is because it is
the principle contract between an object and it's clients.
Specifically the contract is that the object responds to certain
messages, and not to others. This has to be specified before you can
even begin to talk about what state the object is in before or after
it is acted on.

Looking closely in OOSE2. I don't see any mention of the relation of
static typing to DBC. The thing I see is a statement that static
typing is needed for stable, robust systems. There seems to be an
implication that static typing has to come as a precondition to DBC.

Any the experts are in comp.lang.eiffel, so I've forwarded it there.