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Confusing, now-it-happens now-it-doesn't mysteries lurk
in the darkness. When scala packages are declared like this:
package scala.collection.mutable
Then paths relative to scala can easily be broken via the unlucky
presence of an empty (or nonempty) directory. Example:
// a.scala
package scala.foo
class Bar { new util.Random }
% scalac ./a.scala
% mkdir util
% scalac ./a.scala
./a.scala:4: error: type Random is not a member of package util
new util.Random
^
one error found
There are two ways to play defense against this:
- don't use relative paths; okay sometimes, less so others
- don't "opt out" of the scala package
This commit mostly pursues the latter, with occasional doses
of the former.
I created a scratch directory containing these empty directories:
actors annotation ant api asm beans cmd collection compat
concurrent control convert docutil dtd duration event factory
forkjoin generic hashing immutable impl include internal io
logging macros man1 matching math meta model mutable nsc parallel
parsing partest persistent process pull ref reflect reify remote
runtime scalap scheduler script swing sys text threadpool tools
transform unchecked util xml
I stopped when I could compile the main src directories
even with all those empties on my classpath.
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Refactoring the collections api to support differentiation between
referring to a sequential collection and a parallel collection, and to
support referring to both types of collections.
New set of traits Gen* are now superclasses of both their * and Par* subclasses. For example, GenIterable is a superclass of both Iterable and ParIterable. Iterable and ParIterable are not in a subclassing relation. The new class hierarchy is illustrated below (simplified, not all relations and classes are shown):
TraversableOnce --> GenTraversableOnce
^ ^
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Traversable --> GenTraversable
^ ^
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Iterable --> GenIterable <-- ParIterable
^ ^ ^
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Seq --> GenSeq <-- ParSeq
(the *Like, *View and *ViewLike traits have a similar hierarchy)
General views extract common view functionality from parallel and
sequential collections.
This design also allows for more flexible extensions to the collections
framework. It also allows slowly factoring out common functionality up
into Gen* traits.
From now on, it is possible to write this:
import collection._
val p = parallel.ParSeq(1, 2, 3)
val g: GenSeq[Int] = p // meaning a General Sequence
val s = g.seq // type of s is Seq[Int]
for (elem <- g) {
// do something without guarantees on sequentiality of foreach
// this foreach may be executed in parallel
}
for (elem <- s) {
// do something with a guarantee that foreach is executed in order, sequentially
}
for (elem <- p) {
// do something concurrently, in parallel
}
This also means that some signatures had to be changed. For example,
method `flatMap` now takes `A => GenTraversableOnce[B]`, and `zip` takes
a `GenIterable[B]`.
Also, there are mutable & immutable Gen* trait variants. They have
generic companion functionality.
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