Re: proxies: receiver argument and object maps
Le 16/10/2011 23:02, David Herman a écrit :
Forgive me that I've not kept track of where we are in the discussion about
the additional receiver argument.
I think I just found a pretty important use case for the receiver argument.
Say you want to keep some information about a proxy object in a Map or a
WeakMap, and you want the handler to be able to access that information. Then
you're going to need the proxy object to do it.
I suppose you can close over the proxy value:
var proxy;
var handler = { ... proxy ... };
proxy = Proxy.create(handler);
But then you have to make a fresh handler for each instance.
There are 2 different things:
1) the receiver object.
This one may only be useful in case of inheritance:
-
var p = Proxy.create(someHandler);
var o1 = Object.create(p);
var o2 = Object.create(p);
o1.a;
o2.a;
-
here, both o1 and o2 delegates their get to the proxy... so we
thought. Sean Eagan started a thread which conclusion was based on the
semantics of [[Get]], you never call the [[Get]] of the prototype, but
rather its [[GetProperty]] internal. Consequently, you never need the
receiver. Not even for the tricky case of getter/setter binding. See
http://wiki.ecmascript.org/doku.php?id=strawman:proxy_drop_receiver
But in my event as property experiment, I have found that I actually
need that I need the receiver object somewhere to properly implement
inherited events. I'll post on es-discuss as soon as I'm done to make my
case and argue back in favor of receiver.
2) the proxy object
It seems to be what you're describing
Several arguments and experiments have been made proving that proxy as
an argument was necessary for all traps. See
http://wiki.ecmascript.org/doku.php?id=strawman:handler_access_to_proxy
I think we're waiting for the November TC39 meeting for decisions to be
made regarding proxies.
David
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Re: proxies: receiver argument and object maps
D'oh -- of course, you're right. The use case I'm describing wants the proxy,
not the receiver.
Thanks,
Dave
On Oct 16, 2011, at 2:44 PM, David Bruant wrote:
Le 16/10/2011 23:02, David Herman a écrit :
Forgive me that I've not kept track of where we are in the discussion about
the additional receiver argument.
I think I just found a pretty important use case for the receiver argument.
Say you want to keep some information about a proxy object in a Map or a
WeakMap, and you want the handler to be able to access that information.
Then you're going to need the proxy object to do it.
I suppose you can close over the proxy value:
var proxy;
var handler = { ... proxy ... };
proxy = Proxy.create(handler);
But then you have to make a fresh handler for each instance.
There are 2 different things:
1) the receiver object.
This one may only be useful in case of inheritance:
-
var p = Proxy.create(someHandler);
var o1 = Object.create(p);
var o2 = Object.create(p);
o1.a;
o2.a;
-
here, both o1 and o2 delegates their get to the proxy... so we
thought. Sean Eagan started a thread which conclusion was based on the
semantics of [[Get]], you never call the [[Get]] of the prototype, but
rather its [[GetProperty]] internal. Consequently, you never need the
receiver. Not even for the tricky case of getter/setter binding. See
http://wiki.ecmascript.org/doku.php?id=strawman:proxy_drop_receiver
But in my event as property experiment, I have found that I actually
need that I need the receiver object somewhere to properly implement
inherited events. I'll post on es-discuss as soon as I'm done to make my
case and argue back in favor of receiver.
2) the proxy object
It seems to be what you're describing
Several arguments and experiments have been made proving that proxy as
an argument was necessary for all traps. See
http://wiki.ecmascript.org/doku.php?id=strawman:handler_access_to_proxy
I think we're waiting for the November TC39 meeting for decisions to be
made regarding proxies.
David
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Re: proxies: receiver argument and object maps
Le 16/10/2011 23:02, David Herman a écrit :
Forgive me that I've not kept track of where we are in the discussion about
the additional receiver argument.
I think I just found a pretty important use case for the receiver argument.
Say you want to keep some information about a proxy object in a Map or a
WeakMap, and you want the handler to be able to access that information. Then
you're going to need the proxy object to do it.
I suppose you can close over the proxy value:
var proxy;
var handler = { ... proxy ... };
proxy = Proxy.create(handler);
But then you have to make a fresh handler for each instance.
Also, a temporary solution to have access to the proxy without is being
an argument is to put it as a property of the handler. Example:
https://github.com/DavidBruant/HarmonyProxyLab/blob/master/LazyReadCopy/LazyReadCopy.js#L84
Actually, an object is created with the handler as prototype. this
object gets an own proxy property and this is the object that is used
as handler. I think that Tom gets credit for this idea.
David
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Re: proxies: receiver argument and object maps
Yeah, actually, that's roughly what I just ended up doing. I was just playing
with the idea of creating pollution-free dictionaries using proxies, and came
up with this:
https://github.com/dherman/dictjs
The biggest issue, though, is the toString/valueOf one I describe in the other
message I sent this afternoon.
(Well, that and performance, which quite possibly sucks. So this may not be a
viable idea. It was an interesting experiment, anyway.)
Dave
On Oct 16, 2011, at 2:49 PM, David Bruant wrote:
Le 16/10/2011 23:02, David Herman a écrit :
Forgive me that I've not kept track of where we are in the discussion about
the additional receiver argument.
I think I just found a pretty important use case for the receiver argument.
Say you want to keep some information about a proxy object in a Map or a
WeakMap, and you want the handler to be able to access that information.
Then you're going to need the proxy object to do it.
I suppose you can close over the proxy value:
var proxy;
var handler = { ... proxy ... };
proxy = Proxy.create(handler);
But then you have to make a fresh handler for each instance.
Also, a temporary solution to have access to the proxy without is being
an argument is to put it as a property of the handler. Example:
https://github.com/DavidBruant/HarmonyProxyLab/blob/master/LazyReadCopy/LazyReadCopy.js#L84
Actually, an object is created with the handler as prototype. this
object gets an own proxy property and this is the object that is used
as handler. I think that Tom gets credit for this idea.
David
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