Re: 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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>
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