From djsamperi at gmail.com  Wed Feb 16 22:27:43 2011
From: djsamperi at gmail.com (Dominick Samperi)
Date: Wed, 16 Feb 2011 16:27:43 -0500
Subject: [Rd] function call overhead
In-Reply-To: <6441154A9FF1CD4386AF4ABF141A056D21525F40@WMEXOSCD2-N1.bocad.bank-banque-canada.ca>
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Message-ID: <AANLkTikTn30jLoohfgmBNm4xoj9aywKVb4T1M9=uMrDM@mail.gmail.com>

On Wed, Feb 16, 2011 at 1:13 PM, Paul Gilbert
<pgilbert at bank-banque-canada.ca> wrote:
> (subject changed from: RE: [Rd] Avoiding name clashes: opinion on best practice naming ?conventions)
>
> Dominick,
>
> Is this really true? Is there a speed advantage to defining a local function this way, say, within another function, and then calling it within a loop rather than the original? Do you have data on this?
>
> Paul

I worked on an application where a complex characteristic function was
computed over
and over again to compute a Fourier transform, and there was a very
significant performance
penalty to be paid by using myPgk::foo() compared with foo(). It was
recommended on this
list that I try the local assignment trick and it worked great.

Unfortunately this discourages the use of programming styles that are
more explicit and
easier to follow for the human reader. It also complicates the problem
of explicitly specifying
what version of "foo()" you really mean to use.

Dominick

>> -----Original Message-----
>> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-
>> project.org] On Behalf Of Dominick Samperi
>> Sent: February 16, 2011 12:44 PM
> ...
>> Since the resolution of myPkg::foo() occurs at runtime (via a function
>> call) instead
>> of at compile time (as it would in C++), this practice can introduce a
>> significant
>> performance hit. This can be avoided by doing something like:
>> mylocalfunc <- myPkg::foo
>> [tight loop that uses mylocalfunc repeatedly]
>>
>> Here mylocalfunc would not be exported, of course.
>>
>> Dominick
> ...
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[Rd] function call overhead
Dominick Samperi