Ruby

1
Ruby

• Programmers' Best Friend

2
History of Ruby

• Parent Languages
• Perl
• Small Talk
• Lisp
• Ada
• Eiffel

3
History of Ruby

• Founder and Creator
• Yukihiro Matsumoto
• Created
• Feb. 24,1993
• Latest Release
• Version 1.8.4 in December of 2005
• 1.9 in development

4
Why was Ruby Created?

• Make Life much simpler
• Convenience of use for the user, not the
  computer.
• Code should follow the programmer expectations.
  
• Very little surprises.

5
The Power of Ruby

• Massive Libraries
• Multi-threading
• Garbage collection
• Exception handling
• High portability
• Some compilation but will soon see byte-code

6
Naming Conventions

• Similar to Pythons 1st character is a letter or
  an underscore, others are alphanumeric or
  underscore.
• Class names must be capitalized, method names
  must start with a lower case letter.

7
Reserved Words
Programming Ruby The Pragmatic Programmers Guide
8
Data Types

• All data types are classes
• Int, String, Array, Hash,Float
• Int has 2 subcategories
• Bignum
• Fixnum
• Hashes are equivalent to Dictionaries in Python,
  and Arrays are essentially Python Lists.

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Naming Syntax

• Variables can be prefixed with a scope identifier
  to signify their usage.
• No prefix Local.
• _at_ Instance.
• (uppercase) Global.
• _at__at_ Class Variable.
• Uppercase Constant.

_at_size size _at__at_num_instances 0 Config
unix Pi 3.14 tmp a.split
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Naming Conventions

• Built-In modules and classes are Camel Typed.
• MatchData, FileTest, TrueClass, etc.
• Variables are Duck Typed.
• If it walks like a duck and quacks like a duck,
  it must be a duck.
• A variables value determines its type and its
  available set of operations.

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Type Binding

• Everything is Implicit Heap Dynamic.
• Likewise with Python.
• Constants can be reassigned, but with a warning.
• Everything is an object!
• Employs the same dynamic referencing that Python
  uses.

L 1,2,3 h l L0 2 puts h 2,2,3
12
Type Checking

• Rubys variables are weakly typed, just like
  Pythons.
• Even constants can be redefined, however this
  will cause a warning from the interpreter.

13
Blocks

• Rubys blocks generally start with a keyword,
  such as def, class,do, and sometimes
  begin, and end with end.
• Blocks can be passed to functions as a variable.
  This can be useful for creating iterators.

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Blocks (continued)
def fibUpTo(max) i1, i2 1, 1
parallel assignment while i1 lt max
yield i1 i1, i2 i2, i1i2 end end
Passing the block f print f,
fibUpTo(1000) f print f, " "
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Assignment Mechanics

• Fits general syntax found in our book
• lttarget_vargtltassignment_opergtltexprgt
• Uses as operator
• Assigns right side to object on left side

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Assignment Mechanics

• Code

AB123 Agtgt6 Bgtgt6 A(B12)3 Agtgt6 Bgtgt3
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Assignment Mechanics

• Parallel Assignment is allowed as in Python
• This means this Code works
• Otherwise would have to use a temp variable

a, b b, a
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Assignment Mechanics

• Nested Assignments
• gtgtB1,C2,Dnil,E3
• gtgtB1,C2,Dnil,E3
• gtgtB1,C2,D3,E4
• gtgtB1,C2,D3,E5
• gtgtB1,C2,D3,4,E5

B,(C,D),E1,2,3,4
B,(C,D),E1,2,3,4
B,(C,D),E1,2,3,4
B,(C,D),E1,2,3,4,5
B,(C,D),E1,2,3,4,5
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Assignment Mechanics

• and - vs , --
• Ruby allows for the first two symbols but not the
  last. Code

count 2 count - 2 count Error
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Boolean

• Ruby uses the operator to test for equality
• symbol is used for tested equality in the
  Case and When statements.
• Standard lt, gt, lt, gt signs also supported.

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Boolean

• Ambiguous allows for the following
• ! and not
• and and
• and or
• Helpful for programmers learning a second
  language, but decreases readability

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Boolean

• Expression is not wrapped and no colon
• Expression is either followed by a new line or a
  reserved word.
• Indentation is still used for readability
• The reserved word end appears at the end of the
  block of code.

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Boolean

• ltgt symbol is unique to Ruby
• Returns -1,0, or 1
• Code

3ltgt1 1 1ltgt3 2 1ltgt1 0
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Loops

• Similar to python
• Keywords used
• For
• While
• Until
• Object.eachblock
• Num.step , num.upto(n), num.times
• loop

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The For loop
Python
Ruby
for m in list print m
for m in list do print m end
for num in 0..4 print num end
for num in range(5) print num
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While loop
Python
Ruby
while 1 do break if i tyler end
while 1 if i ben break
27
Until

• Resembles a while loop
• Allows more flexibility with the use of
  associated block

until Some condition Body end
28
Object.each

• A method found in most array/string storage type
  objects in ruby.
• Iterates through an object

List t,y,l,e,r List.each x print
x.next
Produces u z m f s
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Num iterations

• Use numbers to iterate a specified amount of
  times
• Possible with FIXNUM class

Produces 0 2 4 6 8 10
0.step(10,2) x print x
5.times do print 1 end
Produces 1 1 1 1 1
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Num.upto(n) compared to C
C
Ruby
0.upto(2) do x print x end
for (int n0 nlt2 n) coutltltn
Both output their respective block variables twice
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loop

• Basic loop statement
• Iterates over a given body
• Requires some sort of break or will run forever

loop Body break
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Other loop constructs

• Retry-start a loop over
• retry if n 1
• Next-used to skip rest of iteration
• next if n 1

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Methods

• Ruby does not support nested method
• Methods are called
• Object.method or object.method()
• Object.method (parameters)
• Also utilize keyword arguments
• Methods are declared in Ruby as follows
• def method
• def method(parameter,parameters2)
• Use of catches any remaining parameters as a
  list
• Must name all functions with lowercase or will be
  a constant not a method.

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Methodology of methods

• In calling a method,Ruby requires
• A receiver --gt receiver
• The Method --gt receiver.method
• Parameters --gt receiver.method(parameters)
• Block --gt receiver.method(parameters)xblock

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Passing to Methods

• Pass By Reference ONLY!
• The word return is NOT used in Ruby.
• The last item modified is returned

def main l 4 a 2 r 1 end
What is returned from the Function to the left?
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Inheritance

• Like C and Python Ruby allows for the
  specialization of classes using inheritance.

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Inheritance

• Code
• Notice that class Diamond is a subclass of Gem
  and is denoted by the lt
• If the super class is not stated ruby assumes it
  to be the Object class

class DiamondltGem def initialize(stone,
karat,value,clarity) super(stone, karat,
value) _at_clarity clarity end
end end
38
Inheritance

• Like Python and C, inheritance allows for the
  programmer to rewrite functions. Ruby will look
  for the definition that is closest at hand
  starting in the sub classes and working up the
  chain into the parent classes.
• The parents function can be called using the key
  word super

39
Inheritance

• Code
• This code calls the parent class Gems function
  common_method instead of the function defined in
  Diamond

class DiamondltGem def common_method
super _at_clarity end end
40
Inheritance

• Single Inheritance only!!!
• Unlike C
• Mixins
• This allows a class to somewhat declare a second
  parent without the drawbacks
• This is done by including a module in a class
  definition

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EVERYTHING OBJECT

• Everything is an object
• Everything belongs to a class
• Example FIXNUM class for numbers
• -5.abs will produce absolute value of -5

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Class Constructs

• Defining classes in Ruby resembles Python
• Classes are an object in Rubys class called
  CLASS.
• There is no use of the word self, except that
  simulated by self
• If a method is missing, Ruby uses the method
  called method_missingon the original receiver.
• Classes and methods are parsed at execution time.

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Notes on Variable scope

• Scope in blocks, loops, and methods
• All variables declared in any of the above are
  lost
• Retained if declared before execution of a block
  or declared global.

ltyler l.each x s t puts x if
t x with the above, we lose s.
s escape block loss ltyler l.each x
s t puts x if t x s is not lost
44
Object specific classes

• Powerful construct that ties a class to a
  specific object
• Quasi-inheritance because object inherits its
  original classes And overrides them with any
  found in the specific class

S somestring classltltS def delete
print self self end
Invoking s.delete Produces somestringsomestring
45
Exception Handling

• Two main forms
• Rescue, Catch and Throw
• Rescue block runs when code in an begin-end block
  raises an exception.
• Catch and Throw are more flexible ways to handle
  exceptions
• Exception Class
• Passed whenever an exception is raised.
• Contains the exception name, a backtrace, and the
  associated error message.

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Rescue

• Can be extended with else, ensure, and retry
  (careful!).
• A rescue example from Programming Ruby.

f File.open("testfile") begin .. process
rescue .. handle error else puts
"Congratulations-- no errors!" ensure
f.close unless f.nil? end
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Catch and Throw
def promptAndGet(prompt) print prompt res
readline.chomp throw quitRequested if res
"!" return res end catch quitRequested do
name promptAndGet("Name ") age
promptAndGet("Age ") sex promptAndGet("Sex
") .. process information end

• An example from Programming Ruby.
• Continues to get input until a ! is input.
• Catch and Throw do not have to be in the same
  scope, more flexible than try and except.

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CGI

• CGI support is a simple way to make Ruby scripts
  available on the Internet
• The Ruby executable is used by the web server
  when a request for a Ruby script is received.
• The CGI module simplifies HTML generation and
  browser interaction.

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CGI Example

• Example script with URL http//mysite.com/ex.rhtml
  ?first_nameben

require "cgi" cgi CGI.new params
cgi.params entered_nameparamsfirst_name cgi.o
ut() do cgi.html() do cgi.head() cgi.body()
do cgi.print ltpgtYou entered , entered_name,
lt/pgt end end end
50
SQL

• Ruby can interface with many popular SQL
  databases when given the proper modules.
• None are available in the default Ruby install.
• Simple MySQL example

require 'mysql' con Mysql.new('localhost',
'my_user', 'secret_pass', 'songs') res
con.query("select from song_info") puts "Artist
\t\t Title" res.each_hash do row puts
row'artist'" \t\t "row'title' end con.close
51
Threading

• Rubys threading implementation is very similar
  to Python threads.
• Ruby also natively supports thread pools,
  synchronization, status control, safety levels,
  etc.

a_thread Thread.new do 10000.times do
print A end end b_thread Thread.new do
10000.times do print B end end a_thread.j
oin b_thread.join puts All done!
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Ruby on Rails

• Rails is an application server built with Ruby.
• Intended to be used alongside MySQL and Apache.
• Portable to wherever its constituents parts run.
• Quick easy creation of dynamic web content.
• Blogs, eCommerce, CMS, etc.

lthtmlgtltheadgtlttitlegtSamplelt/titlegtlt/headgt ltbodygt lt
10.times do gt ltpgtThis is repeated a total of
10 times.lt/pgt lt end gt lt/bodygt lt/htmlgt