Hi Stuart,
According to Liskov substitution principle:
Subtype Requirement: Let ϕ ( x ) be a property provable about
objects x of type T. Then ϕ ( y ) should be true for objects y of type S
where S is a subtype of T.
Let ϕ ( x ) for objects x of type Iterable be: "x.iterator() may be
invoked multiple times, each time starting new iteration".
This clearly holds.
Does ϕ ( y ) hold for objects y of type IterableOnce? Clearly not.
In this respect Iterable should be a subtype of IterableOnce and foreach
loop should be retrofitted to work with IterableOnce.
What do you think?
Regards, Peter
On 3/1/19 3:43 AM, Stuart Marks wrote:
Hi all,
Please review and comment on this proposal to allow Stream instances
to be used in enhanced-for ("for-each") loops.
Abstract
Occasionally it's useful to iterate a Stream using a conventional
loop. However, the Stream interface doesn't implement Iterable, and
therefore streams cannot be used with the enhanced-for statement. This
is a proposal to remedy that situation by introducing a new interface
IterableOnce that is a subtype of Iterable, and then retrofitting the
Stream interface to implement it. Other JDK classes will also be
retrofitted to implement IterableOnce.
Full Proposal:
http://cr.openjdk.java.net/~smarks/reviews/8148917/IterableOnce0.html
Bug report:
https://bugs.openjdk.java.net/browse/JDK-8148917
Webrev:
http://cr.openjdk.java.net/~smarks/reviews/8148917/webrev.0/
Note, this changeset isn't ready to push yet. In particular, it has no
tests yet. However, the implementation is so simple that I figured I
should include it. Comments on the specification wording are also
welcome.
Thanks,
s'marks
