2014-05-22 13:06 GMT-03:00 Camille Teruel <camille.ter...@gmail.com>: > > On 22 mai 2014, at 11:54, stepharo <steph...@free.fr> wrote: > >> >>> In general, we should think about if is would make sense that the language >>> comes with >>> a good proxy model by default. >> >> + 1 >> We should do that with Camille. > > Yes. > Now the problem is to agree on what is a "good model". > There is many use cases for proxies and they come with their own models and > problems. > Here are some requirements I can think of: > > - Uniformity: all objects can be wrapped, even special ones (it's a > technicality but it's still important) > - Interception of all message: currently we cannot intercept #== and > optimized control-flow messages like #ifTrue:ifFalse #to:do:, #whileTrue:, > etc...
> - Encapsulation (a.k.a the self problem): avoid leaking of references to the > target. E.g. "aProxy yourself" should return the proxy not the target. Funny thing is that Glorp proxies materialize the referenced object when they receive #yourself > - Behavioral intercession: Not everything is a message send. What other > events do we want to intercept? IV access is a must-have for me. > - Composition: Wrapping a proxy with another one should work as expected, > i.e. applying both policies in order. > - Performances: intercepting message sends is slow, intercepting iv accesses > is even worse (relying on code instrumentation). We would need VM support. > - Security: It shouldn't be possible to by-pass or corrupt a proxy policy. > - Delimited replacement: Ensure that a proxy is always used in place of its > target throughout the processing of a message send, no matter the alias used > (that is not necessarily "self"). Think about a read-only proxy for example. One thing is a Proxy that ALWAYS sits in between the real object and its consumer forwarding messages or doing any other instrumentation, and a different thing is a Stub which once materialized replaces all references to the proxy with references to the new object (#becomeForward:) and then vanishes (GCed). Having proxies in hashed collections can get very tricky if the hash of the proxy/stub is different from the hash of the materialized object. Esteban A. Maringolo
