On Sunday, 22 July 2012 at 13:39:31 UTC, Philippe Sigaud wrote:
4) How would that allows queries like "Here is class C, give me
all
its available subclasses."? Hmm, wait, I get it: extract
classes from
the module, and recursively from imported modules. From these
classes,
extract the parent classes and so on, until the search ranged
over the
whole inheritance tree. I guess inheritance info could be
standard
enough for std.reflection to provide such a search.
You can't do that without breaking the module system – as long
as a class is not final (and then it doesn't make much sense to
ask for its subclasses anyway), somebody can always extend it in
a module completely separate from the code making the query.
To illustrate what I mean, let's assume you define a class Foo in
a module A. The user imports A from a second module B, and
potentially extends Foo there. Now, if it was possible to get all
possible subclasses in A, this would lead to information leaking
from B to A, while the import graph only allows the other
direction. As a consequence, all kinds of issues related to order
dependence, separate compilation, etc. would arise.
David
