Track the original assets more efficiently in Phase.

Track the original assets more efficiently in Phase.

R=rnystrom@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=28685

[Bob Nystrom, 2013-10-09 17:04:47]

I couple of suggestions but then LGTM.

I'm OK with this patch as-is because the code is not just faster but cleaner. If
this was an optimization patch that made the code more complex, I'd definitely
want to see some empirical data to validate the speed improvement.

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
File pkg/barback/lib/src/multi_set.dart (right):

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
pkg/barback/lib/src/multi_set.dart:17: class MultiSet<E> extends IterableBase<E>
{
Nit, but "multi" is a prefix, not a word, so this should be "Multiset", though
that also looks weird.

How about "Bag"?

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
pkg/barback/lib/src/multi_set.dart:20: final _map = new Map<E, int>();
This assumes that all == E's will never need to be distinguished from each
other. In cases where E is mutable, or where the user cares about identity, this
doesn't do the same thing as a multiset that actually stored each added E
separately.

The semantics here are OK, but should be spelled out. Maybe:

"Elements are considered equal using their == operator. When multiple equal
objects are added, only the first one is retained."

[nweiz, 2013-10-15 21:32:06]

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
File pkg/barback/lib/src/multi_set.dart (right):

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
pkg/barback/lib/src/multi_set.dart:17: class MultiSet<E> extends IterableBase<E>
{
On 2013/10/09 17:04:48, Bob Nystrom wrote:
> Nit, but "multi" is a prefix, not a word, so this should be "Multiset", though
> that also looks weird.
> 
> How about "Bag"?

Renamed to "Multiset".

https://codereview.chromium.org/26598002/diff/1/pkg/barback/lib/src/multi_set...
pkg/barback/lib/src/multi_set.dart:20: final _map = new Map<E, int>();
On 2013/10/09 17:04:48, Bob Nystrom wrote:
> This assumes that all == E's will never need to be distinguished from each
> other. In cases where E is mutable, or where the user cares about identity,
this
> doesn't do the same thing as a multiset that actually stored each added E
> separately.
> 
> The semantics here are OK, but should be spelled out. Maybe:
> 
> "Elements are considered equal using their == operator. When multiple equal
> objects are added, only the first one is retained."

I think it's clear that equality is based on ==, but I'll mention that only the
first copy of equal elements is retained.

[nweiz, 2013-10-15 21:41:05]

Committed patchset #2 manually as r28685 (presubmit successful).