[squeak-dev] Environments

Chris Muller asqueaker at gmail.com
Tue Jun 26 16:05:43 UTC 2012


This namespace solution is just for globals/class names correct?
There could still potentially be method-name conflicts for extensions
to classes in the Smalltalk environment, right?


On Mon, Jun 25, 2012 at 9:11 PM, Colin Putney <colin at wiresong.com> 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
> using.
>
> 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
> here:
>
>   http://www.wiresong.ca/downloads/Environments.zip
>
>
> Flame away!
>
> Colin
>
>
>


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