ruby: an introduction - who am i? maciej mensfeld presented by: maciej mensfeld ruby: an...
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Ruby: An introduction - Who am I?
Maciej Mensfeld
Presented by:
Maciej Mensfeld
Ruby: An introduction
github.com/mensfeld
senior ruby [email protected] ruby [email protected]
Ruby: An introduction – please…
Maciej Mensfeld
Please…
• …ask me to slow down, if I speak to quickly;• …ask me again, if I forget;
• …ask questions, if anything i say is not clear;• …feel free to share your own observations
Ruby: An introduction
Ruby: An introduction – What is Ruby?
Maciej Mensfeld
Ruby WT*?
Ruby pictures
Ruby: An introduction – What is Ruby?
Maciej Mensfeld
What is Ruby?
Ruby is like an Iron Man:
• Shiny;• Red;
• Sometimes quite heavy;• Powerfull;
• Needs electricity;
(and you can use it with Lego Mindstorms)
Ruby: An introduction – What is Ruby?
Maciej Mensfeld
What is Ruby?
• Pure object-oriented programming language (even the number 1 is an instance of class);
• Created by Yukihiro Matsumoto in 1993;• Freely available and open-source;• Syntax is readable and easy to learn;• Being used for text processing, web apps, general system
administration, and AI and math research.• Can be extended with Ruby or low-level C;• Really helpful community;
What Ruby likes?
Maciej Mensfeld
What Ruby likes?
Ruby likes to talk!
Who likes Ruby :-)
Maciej Mensfeld
Who likes to use Ruby?
What Ruby is NOT?
Maciej Mensfeld
What Ruby is not?
• Universal solution for lazy programmers;• Universal solution in general;• Ruby is not an Iron Man ;)• Designed for small applications (with Rails in general);• Python;• Better PHP;• Something that will work on Windows (don’t even thing about it!);
Ruby: An introduction – What is Ruby?
Maciej Mensfeld
Ruby community
A bit more about Ruby…
Maciej Mensfeld
Stay clean and nice!
Ruby: An introduction – What I love in Ruby?
Maciej Mensfeld
Clarity not ceremony – Main program
Java:public class HelloWorld{ public static void main(String args){ System.out.println(„Hello World”); }}
Ruby:puts „Hello World”
Ruby: An introduction – What I love in Ruby?
Maciej Mensfeld
Expressive syntax && objects, objects, objects…
3.times { puts „Ruby is cool”}[„Maciek”, „John”, „Anna”].first #=> „Maciek”[„Maciek”, „John”, „Anna”].last #=> „Anna”attr_accessor :name
„Anna”.class #=> Stringnil.class #=> NilClass1.class #=> Integer{}.class #=> Hash[].class #=> Arrayself.class #=> Object(0..9).class #=> Range
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby syntax – hello world as a function
Hello World! puts „Hello World!”def h puts „Hello World!”end
h => „Hello World!”
Hello YourName! puts „Hello #{name}”
def h(name=„World”) puts „Hello #{name}!”end
h („Maciek”)=> „Hello Maciek!”
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby syntax – classes, methods, objects
Hello YourName! as an object
# Comments starts with „#”class Messenger def initialize(name) # instance variables starts with „@” @name = name end
public def hello puts „Hello #{@name }!” endend
msg = Message.new(„Maciek”)msg.hello #=> „Hello Maciek!”
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby syntax – arrays, hashes (dictionaries)
Arrays names = [‘Maciek’, ‘John’, ‘Freddy’]
names.length #=> 3debts.length #=> 2
Hashes debts={„Maciek”=>1, „John”=> 10}
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby syntax – loops
Ruby:friends.each{|friend| puts friend }
C:for(i=0; i<number_of_elements;i++){ print element[i]}
10.times {|i| puts i }10.downto(1){|i| puts i }
There is no standard „for” loop in Ruby!
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby craziness - symbols
OMG symbols are so weird…
When you ask someone : what are symbols in Ruby? Most programmers will say: they simple are!
A symbol in Ruby is an instance of the class Symbol. A symbol is defined by prefixing a colon with an
identifier. :name, :id, :user
Symbols are most commonly used in creating hashes:h = {:name => "Jayson", :email => „[email protected]"}
The advantage in using symbols is the efficient use of memory. Maximum space taken by a symbol is never more than the space taken by an integer. This is because internally symbol is stored as an integer. In case of strings the memory space depends on the size of the string.
Ruby: An introduction – syntax
Maciej Mensfeld
Ruby craziness - symbolsAlso whenever a string is used in the program, a new instance is created. But for symbols, same identifier points to the same memory location!
puts "name".object_idputs "name".object_idputs :name.object_idputs :name.object_id
Compare:puts "name".object_id == "name".object_idputs :name.object_id == :name.object_id
Interactive Ruby Shell
Maciej Mensfeld
Interactive Ruby Shell
Interactive Ruby Shell (IRB) is a shell for programming in the object-oriented scripting language Ruby. The program is
launched from a command line and allows the execution of Ruby commands with immediate response, experimenting
in real-time.
Interactive Ruby Shell
Maciej Mensfeld
Few simple examples
Type something into IRB and get result of last evaluated expression
Type something into IRB and get result of last evaluated expression
Calculate!
Syntax basics
Maciej Mensfeld
Comments
# Single line comments start with a „#”
# You can always use them like this :-)# So you can have multiply comment lines# This approach is most common
=beginThis is a comment lineit explains that the next line of code displays a welcome message=end
Syntax basics
Maciej Mensfeld
Reserved words
BEGIN do next thenEND else nill truealias elsif not undefand end or unlessbegin ensure redo untilbreak false rescue whencase for retry whileclass if return whiledef in self __FILE__defined? module super __LINE__
The following list shows the reserved words in Ruby. These reserved words may not be used as constant or variable names. They can, however, be used as method names.
Syntax basics
Maciej Mensfeld
Variables
Global variables start with $ Local variables begin with a lowercase letter or _. The scope of a local variable ranges from class, module,
def, or do to the corresponding end or from a block's opening brace to its close brace {}.
There are also class and instance variables – but we will get there in next chapter
Syntax basics
Maciej Mensfeld
Variables
When an uninitialized local variable is referenced, it is interpreted as a call to a method that has no arguments.
Assignment to uninitialized local variables also serves as variable declaration. The variables start to exist until the end of the current
scope is reached. The lifetime of local variables is determined when Ruby parses the program.
Syntax basics
Maciej Mensfeld
Pseudo-Variables
They are special variables that have the appearance of local variables but behave like constants. You can not assign any value to these variables.
• self: The receiver object of the current method.• true: Value representing true.• false: Value representing false.• nil: Value representing undefined.• __FILE__: The name of the current source file.• __LINE__: The current line number in the source file.
Variables are coming…
Syntax basics
Maciej Mensfeld
Conditions - ifif conditional [then]
code...[elsif conditional [then]
code...]...[else
code...]end
You can use if as a conditional modifier…
Syntax basics
Maciej Mensfeld
Conditions - unlessunless conditional [then] code[else code ]end
You can use unless as a conditional modifier…
Syntax basics
Maciej Mensfeld
Case statement
case expression[when expression [, expression ...] [then] code ]...[else code ]end
Syntax basics
Maciej Mensfeld
Loops
Syntax basics
Maciej Mensfeld
Loops
Syntax basics
Maciej Mensfeld
Loops
„For” loop is a great idea but not in Ruby! (use it in PHP)
Syntax basics
Maciej Mensfeld
Strings
Syntax basics
Maciej Mensfeld
Strings
Expression substitution is a means of embedding the value of any Ruby expression into a string using #{ and }:
Syntax basics
Maciej Mensfeld
Numbers
Syntax basics
Maciej Mensfeld
Numbers
Numbers are instances of classes!
Ruby: An introduction
Maciej Mensfeld
THX
Presented by:
Maciej Mensfeld
github.com/mensfeld