From: Jeremy Bopp <jeremy@...>
Date: 2010-10-08T07:55:53+09:00
Subject: Re: Benchmarks Project and example for `||=`

On 10/7/2010 5:11 PM, Intransition wrote:
> 
> 
> On Oct 7, 12:45 pm, Rick DeNatale <rick.denat...@gmail.com> wrote:
>> On Thu, Oct 7, 2010 at 12:05 PM, Jeremy Bopp <jer...@bopp.net> wrote:
>>> The point of comparison profiling like this is to find ways to improve
>>> your code without changing its ultimate function.  Your comparison here
>>> compares two fundamentally different operations
>>
>> It struck me as odd that Trans is benchmarking two different things
>> against each other.
>>
>> As another example,  I just benchmarked the time it takes me to get up
>> out of my sofa and walk to my front door and back at about 30 seconds.
>>  That's over 3 times FASTER than Fernando Alonso's fastest lap of
>> 1:47.976 in the Singapore Grand Prix a couple of Sunday's ago.
>>
>> So does that make me faster than a Ferrari F10, I don't think so, and
>> I doubt that it has a practical significance.
> 
> I think this is a good a reminder as any that it's hard to see what
> someone else is getting at when you're not seeing the use case. There
> is in fact a very good reason for my comparison. I often do:
> 
>   class X
>     def f
>       @f ||= ( do_some_calc_or_lookup )
>     end
>   end
> 
> I like this idiom as it provides the speed bump of caching and yet
> encapsulates the entire procedure for getting the value in one place.
> However, if I am really concerned about squeezing out every bit of
> speed, I would do:
> 
>   class X
>     def initialize
>       @f = ( do_some_calc_or_lookup )
>     end
>     def f
>       @f
>     end
>   end
> 
> The purpose of the benchmark was to see just how much "squeeze" I am
> getting in the exchange.

Take a look at
http://ruby-doc.org/docs/ProgrammingRuby/html/classes.html.  On that
page you'll find some examples for defining a method named "once".
Search for "ExampleDate.once" under the Class and Module Definitions
section.

You can use the "once" method as a directive that will ensure that a
given method which may be expensive to compute is only run 1 time after
which the cached value will be returned.  I made a generalized version
of "once" as suggested there for use in an internal project where I
work.  That way I get the best of delayed computation, clear code, and
fast results for a few methods that really need it.

It might be interesting to profile the performance of a method wrapped
by "once" compared to your other solutions.

-Jeremy