[squeak-dev] Re: Environments
andreas.raab at gmx.de
Tue Jun 26 09:34:23 UTC 2012
Wow. Best approach I've seen so far. Ever. Simple, direct, to the point.
In particular after looking at the code - it is complete enough to be
useful, yet simple enough so that things can be changed if they don't work
out in the way expected. People who don't like it can completely ignore it,
people who want to use it have something to work with. It's just like having
your cake and eating it, too :-)
I would use it.
Colin Putney-3 wrote
> Hi all,
> There's an old joke in the Squeak community about how we have a flame
> war about namespaces every few years and only newbies bring up the
> topic casually. Well, it seems we're overdue, so I'd like to do my bit
> for the community by keeping up the tradition.
> I propose that Squeak 4.4, or perhaps 4.5, include support for more
> than one class with the same name. This will be a modest proposal,
> based on extending Dan's work on environments. The basic idea is this:
> an Environment is an object that implements a policy for binding names
> to objects during compilation.
> This is in direct contrast to the Namespace implementation that
> VisualWorks uses. In VW the global namespace is divided up into a
> dot-delimited hierarchy, and there are mechanisms for resolving
> unqualified names. Environments, in contrast, are more like Newspeak
> modules. There's no universal mapping of names to objects, but rather
> different "points of view," where names resolve differently depending
> on which environment you're in.
> The simplest and most common use for environments is to allow two
> classes with the same name to peacefully co-exist. We currently work
> around this problem with classname prefixes - MC in Monticello or WA
> in Seaside. With environments, we can do away with prefixes by
> creating a separate environment for each prefix that we're currently
> An interesting example of this case that I've run across lately is
> Xtreams. In the original VW version, there's only one class that's
> publicly visible: the Incomplete exception that gets raised when a
> stream operation fails. The rest of the public API to the library is
> provided as extensions to classes in the base system. There's actually
> no need for code that uses Xtreams to refer to any of the stream
> classes. That leaves a lot of room for the implementation of Xtreams
> to change while keeping the API stable, and I'd like to be able to
> take advantage of this design in Squeak. With Environments, that's
> possible: we just create an environment to hold the Xtreams classes,
> import the base system, compile Xtreams, export Incomplete, and import
> Xtreams into our application's environment.
> I've done a preliminary implementation, which lets me create an empty
> environment, file code into it and then browse and modify it with a
> standard browser. There's still lots of work to do, but I want to get
> a consensus among the core developers before tackling it. That way the
> changes can happen in the trunk and we don't have to worry about a
> difficult integration later.
> I've attached a couple of screenshots. The first shows two browsers,
> one browsing the base image, the other browsing an environment with
> Seaside 3.0 loaded. The second is an explorer on the Seaside
> environment. The image where they were taken is available for download
> Flame away!
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