[racket-dev] Class contracts: opaque or transparent?

From: Robby Findler (robby at eecs.northwestern.edu)
Date: Fri Apr 27 15:07:36 EDT 2012

Oh, I see. Yes, this seems like a fine thing to me (making class
contracts be opaque).


On Fri, Apr 27, 2012 at 1:51 PM, Asumu Takikawa <asumu at ccs.neu.edu> wrote:
> On 2012-04-27 13:37:02 -0500, Robby Findler wrote:
>> I think that maybe I still misunderstand? Specifically, if I put an
>> opaque object contract on a value and the contract does not mention
>> 'm', then (send ... m) will be a runtime error
> The opaque class contract wouldn't produce an error on (send ... m) but
> instead when the contract is applied to the class. It's just a first-order
> check that makes sure that
>  "the set of contracted members" = "the set of class members"
>> So, if that's the difference, then what would be the difference of
>> making the class/c contracts for the GUI transparent?
> If all methods have contracts, there is no difference at all. But
> suppose that someone adds a new method and they forget to add a
> corresponding contract. Opaque would then raise an error, transparent
> would not.
> Sorry if I'm being unclear. Let me know if that clears it up.
> Cheers,
> Asumu

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