Re: Optimal use of foreach

While I agree with you on this particular case, cheap hardware is not an
excuse to not do our homeworks and measure performance along the way. Visual
Studio 2005 should strike this point home amongst .NET programmers ... I am
so glad Rico Mariani is leading VS 2010 ;-)

Sébastien
On Wed, Jan 28, 2009 at 12:02 PM, John Warner <[email protected]> wrote:

> If your app depends on the speed difference of a loop on an array you
> should consider tossing more hardware at the issue. Hardware is far
> cheaper than a week or so of programmer time tweaking foreach or for next
> loops :-)
>
> John Warner
>
>
> > -----Original Message-----
> > From: Discussion of advanced .NET topics. [mailto:ADVANCED-
> > [email protected]] On Behalf Of Sébastien Lorion
> > Sent: Wednesday, January 28, 2009 11:23 AM
> > To: [email protected]
> > Subject: Re: [ADVANCED-DOTNET] Optimal use of foreach
> >
> > Well, I said that from memory, so I guess I remembered that bit from
> what I
> > read (as you point out in your blog). Out of curiosity, I popped an old
> > benchmark I made and ya, the results are the same on all .NET versions
> :)
> > Anyway, if your perf depends on the speed difference of a loop construct
> on
> > an array, you need really some serious speed ...
> >
> > Sébastien
> > On Wed, Jan 28, 2009 at 10:20 AM, Greg Young
> > <[email protected]>wrote:
> >
> > > >for loops are usually used in inner loops where you don't want to
> create
> > > >millions of new IEnumerator<T>. They are also slightly faster on
> arrays,
> > > but
> > > >the vast majority of the time, foreach is fine and makes the code
> clearer.
> > >
> > > They are not slightly faster on arrays.
> > >
> > > Please see:
> > > http://codebetter.com/blogs/gregyoung/archive/2006/06/12/146372.aspx
> > > which addresses this point in particular (I believe the originating
> > > point of this misconception was a few people at MS) and
> > > http://codebetter.com/blogs/gregyoung/archive/2006/06/11/146343.aspx
> > > for a more in depth look at how for loops work (its old and there are
> > > some minor revisions to the JIT but most still holds true).
> > >
> > > Cheers,
> > >
> > > Greg
> > >
> > > On Tue, Jan 27, 2009 at 11:51 PM, Sébastien Lorion
> > > <[email protected]> wrote:
> > > > When you use foreach, it actually calls
> > myDictionary.Keys.GetEnumerator()
> > > > which returns a new instance of IEnumerator<T>. That enumerator is
> then
> > > used
> > > > during the loop and Keys is never called again. Open up Reflector
> and
> > > take a
> > > > look at the code, you will better understand what's going on this
> way ;)
> > > >
> > > > for loops are usually used in inner loops where you don't want to
> create
> > > > millions of new IEnumerator<T>. They are also slightly faster on
> arrays,
> > > but
> > > > the vast majority of the time, foreach is fine and makes the code
> > > clearer.
> > > >
> > > > Sébastien
> > > > On Tue, Jan 27, 2009 at 8:43 PM, Mont Rothstein <
> > > [email protected]>wrote:
> > > >
> > > >> When using foreach if the collection is a property will it be
> called on
> > > >> each
> > > >> pass or only once?
> > > >>
> > > >> Can I do:
> > > >>
> > > >> foreach (string key in myDictionary.Keys)
> > > >> {
> > > >> }
> > > >>
> > > >> or will that call Keys each time, therefore requiring that I do:
> > > >>
> > > >> Dictionary<string, string>.KeysCollections keys;
> > > >>
> > > >> keys = myDictionary.Keys;
> > > >>
> > > >> foreach (string key in keys)
> > > >> {
> > > >> }
> > > >>
> > > >> Thanks,
> > > >> -Mont
> > > >>
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> > >
> > >
> > > --
> > > It is the mark of an educated mind to be able to entertain a thought
> > > without accepting it.
> > >
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