Transcript Slajd 1 - Mensfeld

Ruby: An introduction - Who am I?
Ruby: An introduction
Presented by:
Maciej Mensfeld
senior ruby [email protected]
senior ruby [email protected]
[email protected]
dev.mensfeld.pl
github.com/mensfeld
Maciej Mensfeld
Ruby: An introduction – please…
Ruby: An introduction
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
Maciej Mensfeld
Ruby: An introduction – What is Ruby?
Ruby WT*?
Ruby pictures
Maciej Mensfeld
Ruby: An introduction – What is Ruby?
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)
Maciej Mensfeld
Ruby: An introduction – What is Ruby?
What is Ruby?
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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;
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What Ruby likes?
What Ruby likes?
Ruby likes to talk!
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Who likes Ruby :-)
Who likes to use Ruby?
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What Ruby is NOT?
What Ruby is not?
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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!);
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Ruby: An introduction – What is Ruby?
Ruby community
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A bit more about Ruby…
Stay clean and nice!
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Ruby: An introduction – What I love in Ruby?
Clarity not ceremony – Main program
Java:
public class HelloWorld{
public static void main(String args){
System.out.println(„Hello World”);
}
}
Ruby:
puts „Hello World”
Maciej Mensfeld
Ruby: An introduction – What I love in Ruby?
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 #=> String
nil.class #=> NilClass
1.class #=> Integer
{}.class #=> Hash
[].class #=> Array
self.class #=> Object
(0..9).class #=> Range
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Ruby: An introduction – syntax
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!”
Maciej Mensfeld
Ruby: An introduction – syntax
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 }!”
end
end
msg = Message.new(„Maciek”)
msg.hello #=> „Hello Maciek!”
Maciej Mensfeld
Ruby: An introduction – syntax
Ruby syntax – arrays, hashes (dictionaries)
Arrays
names = [‘Maciek’, ‘John’, ‘Freddy’]
names.length #=> 3
debts.length #=> 2
Hashes
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debts={„Maciek”=>1, „John”=> 10}
Ruby: An introduction – syntax
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!
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Ruby: An introduction – syntax
Ruby craziness - symbols
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.
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OMG
symbols are
so weird…
Ruby: An introduction – syntax
Ruby craziness - symbols
Also 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_id
puts "name".object_id
puts :name.object_id
puts :name.object_id
Compare:
puts "name".object_id == "name".object_id
puts :name.object_id == :name.object_id
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Interactive Ruby Shell
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.
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Interactive Ruby Shell
Few simple examples
Type something into IRB and get result
of last evaluated expression
Calculate!
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Type something into IRB and get result
of last evaluated expression
Syntax basics
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
=begin
This is a comment line
it explains that the next line of code displays
a welcome message
=end
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Syntax basics
Reserved words
BEGIN
END
alias
and
begin
break
case
class
def
defined?
do
else
elsif
end
ensure
false
for
if
in
module
next
nill
not
or
redo
rescue
retry
return
self
super
then
true
undef
unless
until
when
while
while
__FILE__
__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.
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Syntax basics
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
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Syntax basics
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.
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Syntax basics
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.
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Variables are coming…
Syntax basics
Conditions - if
if conditional [then]
code...
[elsif conditional [then]
code...]...
[else
code...]
end
You can use if as a conditional modifier…
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Syntax basics
Conditions - unless
unless conditional [then]
code
[else
code ]
end
You can use unless as a conditional modifier…
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Syntax basics
Case statement
case expression
[when expression [, expression ...] [then]
code ]...
[else
code ]
end
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Syntax basics
Loops
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Syntax basics
Loops
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Syntax basics
Loops
„For” loop is a great idea but not
in Ruby! (use it in PHP)
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Syntax basics
Strings
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Syntax basics
Strings
Expression substitution is a means of embedding the
value of any Ruby expression into a string using #{ and }:
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Syntax basics
Numbers
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Syntax basics
Numbers
Numbers are instances of classes!
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Ruby: An introduction
THX
Presented by:
Maciej Mensfeld
[email protected]
dev.mensfeld.pl
github.com/mensfeld
Maciej Mensfeld