> On 27 Feb 2015, at 03:43, Alexandre Bergel <alexandre.ber...@me.com> wrote:
>
> Hi!
>
> I have a near-to-be naive question. Maybe there is something obvious, but I
> cannot see it. Consider the following implementation of a proxy:
>
> -=-=-=-=-=-=-=-=-=-=-=-=
> Object subclass: #MyProxy
> instanceVariableNames: 'object'.
>
> MyProxy >> object: anObject
> object := anObject
>
> MyProxy >> doesNotUnderstand: aMessage
> ^ object perform: aMessage selector withArguments: aMessage arguments
>
> Object >> wrap
> self becomeForward: (MyProxy new object: self; yourself)
> -=-=-=-=-=-=-=-=-=-=-=-=
>
> The problem is with wrap. After the becomeForward:, MyProxy has itself in the
> object variable. Even self is apparently subject to the #become.
>
> It means that the following code loop indefinitely
>
> -=-=-=-=-=-=-=-=-=-=-=-=
> d := Dictionary new.
> d wrap.
> d add: #foo -> 10
> -=-=-=-=-=-=-=-=-=-=-=-=
>
> I know there is Mariano’s library to write proxy. But I still wondering
> whether this could be done simply.
> Any idea how to simply create a proxy?
Hi Alexandre,
You have to store the target and the proxy in different temps, do the become
and (re)set the link between both after. Or in your case, something like:
Object >> wrap
| proxyThenTarget |
proxyThenTarget := MyProxy new.
self become: proxyThenTarget.
“Now self is the proxy"
self object: proxyThenTarget.
^ self
Note that by subclassing Object many messages won’t be intercepted. With your
dictionary example it means that you cannot intercept #at: . Subclassing
ProtoObject reduces the number of such messages.
Also one can bypass these methods by sending #doesNotUndestand: to the proxy.
In the end all depends on your requirements: do you care about uniformity (all
messages must be intercepted), composition of proxies, security (no target
leaks, no interception bypass), what operations do you want to intercept (just
message sends or iv accesses in addition), etc...
For most cases Ghost is the way to go.
Camille
>
> Cheers,
> Alexandre
>
> --
> _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
> Alexandre Bergel http://www.bergel.eu
> ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.
>
>
>
>
