Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Programming
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Databases
Mail Systems
openSolaris
Eclipse Documentation
Techotopia.com
Virtuatopia.com

How To Guides
Virtualization
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Windows
Problem Solutions

  




 

 

Ruby - Nuts and bolts

Object initialization
Prev
Contents
Contents
Contents
Next

 Ruby user's guideNuts and bolts 

This chapter addresses a few practical issues.

Statement delimiters

Some languages require some kind of punctuation, often a semicolon (;), to end each statement in a program. Ruby instead follows the convention used in shells like sh and csh. Multiple statements on one line must be separated by semicolons, but they are not required at the end of a line; a linefeed is treated like a semicolon. If a line ends with a backslash (\), the linefeed following it is ignored; this allows you to have a single logical line that spans several lines.

Comments

Why write comments? Although well written code tends to be self-documenting, it is often helpful to scribble in the margins, and it can be a mistake to believe that others will be able to look at your code and immediately see it the way you do. Besides, for practical purposes, you yourself are a different person within a few days anyway; which of us hasn't gone back to fix or enhance a program after the passage of time and said, I know I wrote this, but what in blazes does it mean?

Some experienced programmers will point out, quite correctly, that contradictory or outdated comments can be worse than none at all. Certainly, comments shouldn't be a substitute for readable code; if your code is unclear, it's probably also buggy. You may find that you need to comment more while you are learning ruby, and then less as you become better at expressing your ideas in simple, elegant, readable code.

Ruby follows a common scripting convention, which is to use a pound symbol (#) to denote the start of a comment. Anything following an unquoted #, to the end of the line on which it appears, is ignored by the interpreter.

Also, to facilitate large comment blocks, the ruby interpreter also ignores anything between a line starting with "=begin" and another line starting with "=end".

#!/usr/bin/env ruby

=begin
**********************************************************************
  This is a comment block, something you write for the benefit of
  human readers (including yourself).  The interpreter ignores it.
  There is no need for a '#' at the start of every line.
**********************************************************************
=end

Organizing your code

The ruby interpreter processes code as it reads it. There is nothing like a compilation phase; if something hasn't been read yet, it is simply undefined.

# this results in an "undefined method" error:

print successor(3),"\n"

def successor(x)
  x + 1
end

This does not, as it might seem at first glance, force you to organize your code in a strictly bottom-up fashion. When the interpreter encounters a method definition, it can safely include undefined references, as long as you can be sure they will be defined by the time the method is actually invoked:

# Conversion of fahrenheit to celsius, broken
# down into two steps.

def f_to_c(f)
  scale(f - 32.0)  # This is a forward reference, but it's okay.
end

def scale(x)
  x * 5.0 / 9.0
end

printf "%.1f is a comfortable temperature.\n", f_to_c(72.3)

So while this may seem less convenient than what you may be used to in Perl or Java, it is less restrictive than trying to write C without prototypes (which would require you to always maintain a partial ordering of what references what). Putting top-level code at the bottom of a source file always works. And even this is less of an annoyance than it might at first seem. A sensible and painless way to enforce the behavior you want is to define a main function at the top of the file, and call it from the bottom.

#!/usr/bin/env ruby

def main
  # Express the top level logic here...
end

# ... put support code here, organized as you see fit ...

main # ... and start execution here.

It also helps that ruby provides tools for breaking complicated programs into readable, reusable, logically related chunks. We have already seen the use of include for accessing modules. You will also find the load and require facilities useful. load works as if the file it refers to were copied and pasted in (something like the #include preprocessor directive in C). require is somewhat more sophisticated, causing code to be loaded at most once and only when needed. There are other differences between load and require; refer to the language manual or the FAQ for more information.

That's it...

This tutorial should be enough to get you started writing programs in Ruby. As further questions arise, you can dig into the reference manual to learn about ruby in more depth. The FAQ and library reference are also important resources.

Good luck, and happy coding!


Object initialization
Prev
Contents
Contents
Contents
Next

 
 
  Published under the terms of the OpenLDAP Public License Design by Interspire