From: "Iñaki Baz Castillo" <ibc@...>
Date: 2009-12-06T10:48:31+09:00
Subject: Why doesn't Ruby "compile" strings?

Hi, the following code:

-------------------
#!/usr/bin/ruby

require "benchmark"

HELLO_WORLD = "hello world"

1.upto(4) do

	print "Benchmark using HELLO_WORLD:   "
	puts Benchmark.realtime { 1.upto(500000) {|i| HELLO_WORLD.upcase } }

	print "Benchmark using \"hello_world\": "
	puts Benchmark.realtime { 1.upto(500000) {|i| "hello_world".upcase } }

	print "Benchmark using 'hello_world': "
	puts Benchmark.realtime { 1.upto(500000) {|i| 'hello_world'.upcase } }
	
end
-------------------


gives these results:

--------------------
Benchmark using HELLO_WORLD:   1.1907217502594
Benchmark using "hello_world": 1.53604388237
Benchmark using 'hello_world': 0.816991806030273
Benchmark using HELLO_WORLD:   0.599252462387085
Benchmark using "hello_world": 0.814466714859009
Benchmark using 'hello_world': 0.812573194503784
Benchmark using HELLO_WORLD:   0.595503330230713
Benchmark using "hello_world": 0.813859701156616
Benchmark using 'hello_world': 0.813681602478027
Benchmark using HELLO_WORLD:   0.594272136688232
Benchmark using "hello_world": 0.815742254257202
Benchmark using 'hello_world': 0.811828136444092
--------------------


Let's take the last result so Ruby is "entirely loaded":

--------------------
Benchmark using HELLO_WORLD:   0.594272136688232
Benchmark using "hello_world": 0.815742254257202
Benchmark using 'hello_world': 0.811828136444092
--------------------


This clearly shows that using a constant string is faster than using a string 
writen into the script. So I wonder: why doesn't Ruby "precompile" internally 
the strings appearing in the script?

This is, when Ruby interpreter is parsing the script and founds "hello_world", 
couldn't it create the string *just once* and keep in memory forever so next 
time same string is accessed Ruby doesn't need to initiate it?
Is it imposible due to the design of Ruby?

PS: I don't know if other languages (Python, PHP, Perlo...) do it or not.


-- 
Iñaki Baz Castillo <ibc@aliax.net>