From: Daniel Carrera <dcarrera@...>
Date: 2002-11-21T14:07:27+09:00
Subject: [FAQ] Interpreted vs compiled [FAQ] defining methods anywhere

Hello,
Gavin suggested I compile the answers to my questions into FAQs.  Here
they are:

1.- [FAQ] Is Ruby interpreted or compiled?

Ruby is interpreted - The parser creates an a syntax tree that is walked.
Future plans for Ruby are to move it closer to a compiled language.
These include projects to create a RubyVM (Rite, or Ruby 2.0) as well as
Cardinal (Ruby frontend for the ParrotVM).
Being interpretted does affect the speed of execution to some extent, but
Ruby actually does pretty well in the language shootout rankings.
Generally not as fast as Perl, but not too much slower.

2.- [FAQ] Why can't I define my methods anywhere?

Methods are defined at run-time.  Therefore, (unlike Perl) a method cannot
be used before it is defined.  This will not work:

greeting("Daniel")
def greeting(name)
	puts "Hello #{name}"
end

But this will:

def greeting(name)
	puts "Hello #{name}"
end
greeting("Daniel")

This is a trade-off.  It allows you great freedom to modify methods during
program execution.  For instance:

#!/usr/bin/ruby

define greeting(name)
	puts "Hello #{name}"
end
greeting("Daniel")

define greeting(name)
	puts "Hi #{name}"
end
greeting("Daniel")

Will print:

Hello Daniel
Hi Daniel

Whereas, the Perl equivalent:

#!/usr/bin/perl

sub greeting {
	print "Hello $_[0]\n";
}
greeting("Daniel")

sub greeting {
	print "Hi $_[0]\n";
}
greeting("Daniel")

Will print:

Hi Daniel
Hi Daniel

Because Perl's subroutines are defined at compile-time.

In Ruby you als ohave the optino of using classes:

  class Greeting
    def initialize
      hello
    end

    def hello
      puts "Hi!"
    end
  end

  Greeting.new             # -> Hi!


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