[please please please try quoting a little less]
On Thu, Dec 5, 2013 at 11:50 AM, David Bruant <bruan...@gmail.com> wrote:
> From reading this thread I feel I'm severely lacking the proper background,
> but I'd like to try a question anyway.
>
> 1.3 Use Case: Contracts:
>>
>> During maintenance, the programmer may add contracts to a program as
>> understanding improves.
>
> What does "add contracts" mean? "Add" contracts to a given object/function
> which already have one? Add contracts to things that didn't have any
> beforehand?
Contracts mediate the interaction between different components. So to
"add contracts to a program", a programmer specifies that a particular
interaction in the program occurs through a contract.
This is best modeled using a form like I mentioned in an earlier message:
let newValue = applyContract(contract, value);
Note that `value` is still accessible, of course.
It's useful to use the intuition of legal contracts (hence the name).
If you and I sign a contract for you to use my car, that doesn't
change the car, but it constraints the interaction between you and the
car.
>> Clearly, the addition of a new contract must not change a program
>> execution that respects the contract already.
>
> Agreed.
>
>> In this scenario, the program executes in a mix of original objects and
>> proxy objects.
>
> I don't understand why. The way I see it, an object with a contract is an
> object replaced in the runtime by a proxy which handler implements the
> contract. When I write "replace", I mean that the object constructed as a
> proxy. Otherwise, there are places where the contract can't and won't be
> enforced.
> By my definition, the original object is only available to the proxy as its
> target and no other context. Also, even if piling contracts, only one proxy
> is available in the end (previous proxy becomes target of next contract
> proxy).
> Or is the contract different based on where the object is sent? If the
> answer is yes, is it really the same object? Isn't it rather a façade to the
> target (and should effectively be a different object, most likely a proxy)
As is hopefully clear above, this isn't how contracts work. Applying a
contract to an object doesn't change the object.
Sam
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