Ruby on rails Part 1 - Introduction to Ruby
Table of content
- Introduction
- Installation
- Basics IRB
- Printing to console
- Comments
- Variables
- Data types
- Chomp
- User input
- Data structure
- Arrays
- Hash
- Set
- Branching
- Loops
- Methods
- Class and objects
Introduction
Ruby programming language is a pure object oriented programming language. Ruby is a scripting language designed by Yukihiro Matsumoto (Matz). It was designed in 1993. Just like Smalltalk, Ruby is a perfect object-oriented language. with much easier syntax than Smalltalk.
Features of Ruby:
- Ruby is an open-source and is freely available on the Web, but it is subject to a license.
- Ruby is a general-purpose, interpreted programming language.
- Ruby is a true object-oriented programming language.
- Ruby is a server-side scripting language similar to Python and PERL.
- Ruby has a clean and easy syntax that allows a new developer to learn very quickly and easily.
- Ruby has a rich set of built-in functions, which can be used directly into Ruby scripts.
Installation
- For Ubuntu/Linux
To install ruby using apt, run the command in terminal :
$ sudo apt-get install ruby-full
To check the path of the ruby installation :
$ which ruby
To check the version of the ruby installed :
$ ruby --version
2. For Windows
Download
ruby installer from here . Run it and
follow the instructions.
3. For MacOS: we can use brew to install ruby
$ brew install ruby
Basics IRB
Ruby has an interactive ruby shell called irb. Type irb in the terminal and it opens the shell.
Print to console
Comments
Comments in Ruby start with # symbol.
# This is a single line comment
= This is a multi line
comment =
Variables
Primitive Data Types
Integer: Denotes an integer
Float: Denotes fractional numbers
String: Denotes a sequnce of characters
Boolean: Denotes true or false value
Symbols: Similar to strings, start with a : and are immutable. Example - :someThing, :123
Array: Collection of similar objects
Hashes: Key-Value pair
Chomp
This method
removes record separators (/r, /n, etc) or the specified sub-string from the end
of the string.
str = ‘string\r\n’
puts str.chomp # Prints string without /r and /n
puts str.chomp(‘ng’) # Prints stri
Get user input
We have a gets that reads data from the console. The type of the data is string.
varName = gets
# Gets user input as string and stores it in varName
varName1 = gets.chomp.to_i
# Gets user input as string then converts it to int and then stores it in varName1
Data structure
Array
Array is an indexed sequential data structure. He is an heterogeneous data structure.
arr = [1,2,3] # Creates array with 3 elements
arr = Array.new(10) # Creates empty array of size 10
arr.push(4) or arr<<(4) # Adds element to the end
arr.unshift(5) # Adds element to the start
arr.insert(index, element) # Adds element at the specified index
arr[index] # Returns element at index
Hash (Dictionary/key-value pair)
Hash data structure is a key-value pair data structure. There are three ways to declare a Hash. We can access the values by using the key in the hash.
hash1 = { “Key1” => “Value1”, # defining Hash
“Key2” => “Value2”,
“Key3” => “Value3”
}
hash2 = Hash.new #Another way of defining Hash
hash3 = Hash.new(“Default Value”)
#This default value is returned for all keys whose values aren’t defined yet
hash3[5] #This will return Default Value
hash3[9] #This will return Default Value
puts hash1[“Key2”] # Prints Value2
hash1[“Key4”] = “Value4” # Add new key value pair
Set
Set is data structure that hold unique values. It internally implements a Hash data structure. It hold only unique values.
set1 = Set.new #Creates an empty set
set2 = Set[1,2] #Creates new set with 2 elements
set3 = [1,2,3,4].to_set #Converts an array to set
set1.add(1) #Add new element to the set
set2.merge([2,3,4]) #Merges an array with the set
set2.delete(2) #Deletes 2 from set2
If-Else
if 1 > 2
puts “No!”
elif 0 > 1
puts “Noo!”
else
puts “Yes”
end
Switch case
arr = [1,2,3,4]
case arr
when 1
puts 1
when 2
puts 2
when 3
puts 3
else
puts "else"
end
Loops
for varName in 0..5 # For each item in range 0 to 5
puts varName # print 0 1 2 3 4 5
end
for varName in [1,2,3,4] # For each item in range 1 to 4
puts varName # print 1 2 3 4
end
while condition == true do # While some condition is true
puts “Inside loop” # Execute this statement
end
loop do # This is a do-while loop
puts “Hello” # Execute the loop first
if condition == false # Then check for the condition
break # Break out of the loop if false
end
end
until and unless
i = 1
until i == 10
puts i
i += 1
end
x =3
unless x < 5 # Opposite of if. Executes when condition is false
puts "Inside unless" # Similar to “if not” or “if !”
else
puts "Inside unless-else"
end
Methods
Methods are code blocks in Ruby. They can be parameterized and return multiple values.
def methodName(parameterName) # Creates a method with 1 parameter
puts "Hello #{parameterName}" # Prints the parameter name
return "Done Printing" # Returns “Done Printing”
end
def methodName(Everyone) # Calling the method and passing a string
def method1(val1 = "default1") # Default parameter example
puts default1
end
def method2 # Can skip () after methodName. Even with arg
i = 1
j = 2
k = 3
return i, j, k # Can return multiple values
end
They can take variable number of arguments.
def method3 *args # Accepts multiple and stores it in array
for i in 0..args.length
puts i
end
end
Classes and Objects
class ClassName
@name = '' #This is an instance variable
def initialize(name)
@name = name
end
def getName()
puts "Name is #{@name}"
end
end
obj = ClassName.new("Everyone")
obj.getName()
A variable
starting with @ is an instance variable. That means its value is specific to
an object whereas a variable starting with @@ is a class variable (Static variable).
The value of such variable is accessible to all instances of the class.
Important Functions
objectName.methods.sort # Returns all available methods for this object (Sorted)
objectName.class # Specifies the type of object
objectName.object_id # Returns memory address of the object
break and next
break => This keyword is used to break out of a loop/condition statement
next => This is similar to continue in other languages. Used to skip the current iteration
retry and redo
redo is used to repeat the current iteration of the loop
retry is used to restart the execution of
the block from the start (1st iteration). Can only be used in
exception handling.
for i in 0..5 # Loop should print 0 to 5
puts i # Prints till 3
redo if i==3 # Now the loop gets stuck at value i == 3. Hence an infinite loop
end