On Oct 31, 2007, at 3:46 AM, Maciej Stachowiak wrote:
I notice some seemingly duplicate features that will perhaps become
more clear on closer reading of the spec. For instance I see all three
of namespace, package and unit productions in the grammar. With my
limited imagination it's hard to think of how those could be three
interestingly different features.
What's the Sesame Street song? "... one of these things is not like
the other, one of these things just doesn't belong."
You are not alone in wondering about these three -- this has come up
at past TG1 meetings and we went ahead and implemented to get
experience. Michael O'Brien has a small-device implementation that
he's posted about here. He may have useful feedback.
This may help separate namespaces and units:
* A namespace is a qualifier on property name (a string in general in
ES1-3). It's a prefix to apply to unqualified identifiers used by a
block in which a 'use namespace N' pragma occurs at the top. There
are sane rules about ordering and ambiguity errors, covered briefly
in the overview. As you can see from the RI, namespaces are used
heavily. One benefit is to avoid incompatible name pollution of
unqualified identifiers in the standard objects and the global object.
* A program unit is an explicit reflection of the Program
production's semantics from ES1-3. When you see a program unit body's
closing brace, the steps in ES3 Chapter 10.2, plus ES4 steps like
those, kick in. You can nest units, and a server framework can expand
them server side when they are stated without bodies, but with
locators that point to the body in question. This preserves accurate
source coordinates for errors coming from nested units, and avoids
downloading too many small files. See the proposal for more detail.
These two are genuinely different, orthogonal, and useful things, I
think.
* Packages are built on namespaces, and unlike program units they are
open-ended. You can keep adding to a package (someone correct me if
I'm wrong), by writing
package acme.widgets {
...
}
several times in a row. As the overview notes, a package has two
namespaces, package-public and package-internal. There's an import
directive for pulling some or all of the public names of a package
into another scope.
/be
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