From: Timothy Hunter <cyclists@...>
Date: 2005-10-30T00:02:06+09:00
Subject: Re: determining whether an object is an immediate?

Eric Mahurin wrote:
> This is be best I could come up with for determining whether an
> object is an immediate (Fixnum, Symbol, false, true, nil,
> others?):
> 
> begin
>   obj.clone
>   # clone worked - not an immediate
> rescue TypeError
>   # clone failed - immediate
> end
> 
> Anybody have a better way?  If the above is the best, seems
> like an Object#immediate? would be nice to have.
> 
I seem to remember that begin/rescue is extremely slow, so since we know 
up front what all the immediate classes are I guessed that it would be 
faster just to test for them in a case expression. I put together a 
benchmark test that confirms my suspicion. Results first, then the test. 
I ran the test on my Powerbook.

me$ ruby test.rb
         user     system      total        real
rescue  2.040000   0.130000   2.170000 (  2.527118)
case    0.220000   0.010000   0.230000 (  0.240941)

Here's the test code. The OBJECTS array contains 5 immediate objects and 
  5 non-immediate objects. Of course, with the "rescue" approach you get 
a clone of the non-immediate object and in the "case" approach you 
don't, but I'm assuming that you don't need the clone.

require 'benchmark'
include Benchmark

OBJECTS = [1, [], :sym, "astring", true, {}, false, 1..3, nil, /x/]
ITERATIONS = 10000

bm(2) do |x|
	x.report("rescue") do
		ITERATIONS.times do
			OBJECTS.each do |obj|
				begin
					obj.clone
				rescue
					# nothing
				end
			end
		end
	end
	
	x.report("case  ") do
		ITERATIONS.times do
			OBJECTS.each do |obj|
				case obj
					when Fixnum, Symbol, TrueClass, FalseClass, NilClass
						# nothing
					else
						# nothing
				end
			end
		end
	end
  	
end