Ruby: An introduction

Ruby: An introduction
-

Who

am

I?

Maciej Mensfeld

Presented
b
y
:


Maciej Mensfeld

Ruby: An introduction

maciej@mensfeld.pl

dev.mensfeld.pl

github.com
/
mensfeld

senior
ruby

developer@araneo.pl

senior
ruby

developer@furioustribe.com

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”

a
ttr_accessor

:
name

„
Anna”.class

#=>
String

nil.class

#=>
NilClass

1.class #=>
Integer

{}.
class

#=>
Hash

[].
class

#=>
Array

self.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

}!”


end

end

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

#=> 3

debts.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 => „
test@gmail.com
"}

T
he

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

-

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

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

=begin

This is a comment line

it explains that the next line of code displays

a welcome message

=end

Syntax

basics

Maciej Mensfeld

Reserved

words

BEGIN

do

next

then

END

else

nill

true

alias

elsif

not

undef

and

end

or

unless

begin

ensure

redo

until

break

false

rescue

when

case

for

retry

while

class

if

return

while

def

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

-

if

if conditional [then]



code...

[
elsif

conditional [then]



code...]...

[else



code...]

end

You

can

use

if

as a
conditional

modifier
…

Syntax

basics

Maciej Mensfeld

Conditions

-

unless

unless 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
b
y
:


Maciej Mensfeld

maciej@mensfeld.pl

dev.mensfeld.pl

github.com
/
mensfeld