On 12-Aug-12 14:35, Jonathan M Davis wrote:
On Sunday, August 12, 2012 03:20:49 Walter Bright wrote:
On 8/12/2012 1:36 AM, Johannes Pfau wrote:
Probably we should distinguish between finish functions which destroy
the internal state and peek functions which do not modify the internal
state.
I worry about too many parts to an interface.
A peek function needs a really strong use case to justify it.
The big question is whether it's merited in output ranges in general. A
function could still be worth having on an individual type without making
sense for output ranges in general as long as it's not required to use the
type.
However, I really don't think that peek makes sense for output ranges in
general. Most of the time, you're just writing to them and not worrying about
what's already been written. It's basically the same as when you write to a
stream. I don't think that I've seen a peek function on an output stream.
Agreed. Current appender has .data (a-la peek) just because of
implementation details that allow it. In fact there was a pull for
Phobos including s better Appender (that would end up being a Builder I
guess) that doesn't allow to peek at array in creation until the very
end but provides much better performance profile.
BTW what's happened with that pull? I recall github nickname sandford,
but can't recall whose awesome work that was. I'd love to see it make
its way into Phobos.
And I really don't think that peek makes sense in the context of hashes. You
don't care what a hash is until it's finished. And once it's finished, it really
doesn't make sense to keep adding to it. I don't know why you'd ever want an
intermediate hash result.
Having partial hashes over data is very useful e.g. for fast binary diff
algorithms. However it requires specific form of hash function (so that
you can look at result) and/or operating at specific block granularity.
If you call finish, you're done. And if finish gets called again, it's just like
if you call popFront after an input range is empty. The behavior is undefined
(though popFront - or finish in this case - probably has an assertion for
checking in non-release mode). I really don't think that it's all that big a
deal.
Agreed. finish seems as a good name because indicates that it's an end
of operation. But consider that hash accumulator can be reset after
finish and reused (unlike say network stream).
--
Dmitry Olshansky
