Ruby Tutorial: Ruby Intro

Introduction to Ruby for Programmers

This section is intended as a brief, lightweight overview of the Ruby language; following sections will cover all these topics in much more detail. Students are encouraged to ask questions, but instructors are encouraged to answer, "We'll cover that later."

(Originally based upon Ruby Quickstart for Refugees but improved by many.)

Ruby vs. Rails

Ruby is a Language

Rails is a Framework

Rails is written in Ruby

Ruby Philosophy

"People want to express themselves when they program."

"They don't want to fight with the language."

"Programming languages must feel natural to programmers."

"I tried to make people enjoy programming and concentrate on the fun and creative part of programming when they use Ruby."

 - Matz (Yukihiro Matsumoto)

Ruby Philosophy, Applied

  • Ruby has a humane interface
    • many ways to do things
  • Ruby favors readability and variety over concision and perfection
  • sometimes makes code hard to understand (but usually makes it easier)
  • contrast to minimal interface
    • one (or a few) "right" ways to do things
    • Python has a minimal philosophy

Many Rubies

  • Ruby 1.0 released in 1996
    • Fully Open Source
  • Many implementations
    • MRI
      • REE
      • Kiji
    • JRuby
    • Rubinius
    • MagLev
    • MacRuby
    • IronRuby

Versions common today

  • MRI 1.8.7
  • MRI 1.9.2
  • JRuby

Ruby Language Overview

  • Dynamically typed
  • Interpreted
  • Can be modified at runtime
  • Object oriented
  • Blocks / lambdas / closures
  • Perl-like regular expressions
  • Closely tied to shell & OS

IRB: Interactive RuBy

@@@ ruby
$ irb
>> 4
=> 4
>> 4+4
=> 8

Please fire up irb on your computer and try this out!

Everything evaluates to something

@@@ ruby
>> 2 + 2
=> 4

>> (2+2).zero?
=> false

>> "foo" if false
=> nil

>> puts "foo"
foo
=> nil

Hash mark comments, like perl

@@@ ruby
# is a comment
2 + 2 # is a comment

Optional semicolons, parens, and return

These are equivalent:

@@@ ruby
def inc x
  x + 1
end

def inc(x)
  return x + 1;
end

def inc(x); x + 1; end

Line Break Gotcha

@@@ ruby
x = 1 + 2
x #=> 3

x = 1
  + 2      
x #=> 1

Solution: always put operators on top line

x = 1 +
    2      
x #=> 3

Use parens when you need them

@@@ ruby
>> "Hello".gsub 'H', 'h'
=> "hello"

>> "Hello".gsub("H", "h").reverse
=> "olleh"

Variables are declared implicitly

@@@ ruby
first_name = "Santa"
last_name = "Claus"
full_name = first_name + last_name
#=> "SantaClaus"

String interpolation

@@@ ruby
"boyz #{1 + 1} men"
=> "boyz 2 men"
  • Any Ruby code can go inside the braces
  • It gets evaluated and stuck inside the string

Built-in Types

  • Numbers
    • 42
  • Booleans
    • true
    • false
  • Strings
    • "apple"
    • 'banana'
  • Symbols
    • :apple
  • Arrays
    • ["apple", "banana"]
  • Hashes
    • {:apple => 'red', :banana => 'yellow'}
  • Ranges
    • (1..10)

Functions

@@@ ruby
def add(a,b)
  a + b
end

add(2, 2) 
#=> 4
  • Note: no 'return' required

Classes and methods

@@@ ruby
class Calculator
  def add(a,b)
    a + b
  end
end
  • a function inside a class is called a method

bang and question methods

  • method names can end with ! or ?
    • ! means "watch out!"
    • ? means "boolean"

equal, double-equal, and threequal

  • x = 1 means "put the value 1 in the variable x"
  • x == 2 means "true if x is 2, otherwise false"
  • x === 3 means the same as == but sometimes more

Ruby syntax cheatsheet

cheatsheet

(The Well-Grounded Rubyist, p. 5, section 1.1.2)

Ruby identifiers

  • local_variable - start with letter or underscore, contain letters, numbers, underscored
  • @instance_variable - start with @
  • @@class_variable - start with @@
  • $global_variable - start with $
  • Constant - start with uppercase letter
  • method_name? - same as local, but can end with ? or ! or =
  • keywords - about 40 reserved words (def) and weirdos (__FILE__)
  • literals - "hi" for strings, [1,2] for arrays, {:a=>1, :b=2} for hashes

Ruby Naming Conventions

methods and variables are in snake_case

classes and modules are in CamelCase

constants are in ALL_CAPS

Standard is better than better.

-- Anon.

Variable Scopes

@@@ ruby
var   # local variable (or method call)
@var  # instance variable
@@var # class variable
$var  # global variable
VAR   # constant

Messages and Methods

  • an object is referenced by a variable or a literal
  • the dot operator (.) sends a message to an object
  • an object receives a message and invokes a method
  • with no dot, the default object (self) is the receiver

Classes

  • A class defines a group of behaviors (methods)
  • Every object has a class, Object if nothing else

load and require

  • load inserts a file's contents into the current file
  • require makes a feature available to the current file
    • skips already-loaded files
    • omits the trailing .rb
    • can also be used for extensions written in C (.so, .dll, etc.)
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