1. Class vs Module in Ruby

2. Ruby Array - Index

• take(n) : The first n elements of the array can be accessed using this method.
• drop(n) : Everything but except the first n elements of the array can be accessed using this method.

Example:

array = [1,2,3,4,5,6,7,8,9]
array.drop(2) => Result: 3,4,5,6,7,8,9

3. Ruby Array - Addition

• push => Add element at the ending of the array.
• unshift => Add element at the beginning of the array.

4. Rubby Array - Selection

• Non-Destructive Selection: select, reject, drop_while
• Destructive Selection: select!, reject!, delete_if, keep_if

5. Ruby Syntax

• All Ruby files will have extension .rb .
• Whitespace: Ignore in Ruby, just use to exaplain ambigous statement.
• Ruby indentifiers are case sensitive.
• Comment:
  • Single line: #
  • Multiple lines:

    =begin
    =end
    

6. Ruby Variables

• Local variable: Begin with lowercase letter or _ character.
• Instance variable: Begin with @ character.
• Class variable: Begin with @@ character.
• Global variable: Begin with $ character.
• Constant: Uppercase letter and can change value after initialize.

7. Ruby String

• Define a string in Ruby start with '' or "" .
• Defference between '' and "" .
  • '' : Don't allow substitution and backslash notation.
  • "" : Allow substitution and backslash notation. And can insert the value of any Ruby expression into a string using the #{} .

8. Ruby Operators

• **, example 2**3 =8 .
• <=> : Combined comparision operator. Returns 0 if first operand equals second, 1 if greater than, -1 if less than.
• Difference between == and eql? operator:
  • == : Compare only value.
  • eql? : Compare both value and type.
• Parallel assignment : It is also useful for swapping the values held in two variables. Example:

a = 1
b = 2
c = 3
a, b = b, c

=> a = 2, b = 3, c = 3.

• .. : Include.
• ... : Exclude.

9. Ruy case statement

case expr0
when expr1, expr2
   stmt1
when expr3, expr4
   stmt2
else
   stmt3
end

10. Ruby Method

• Variable Number of Parameters: Ruby allows declare methods that work with a variable number of parameters, meaning this method, we can pass any parameters, without specified parameter.

Example:

def foo(*params)
end

So, we can call this method:

foo("banana", "orange")
foo("pig")
...

• Difference between instance method and class method and module method :
  • Instance Method: Provides functionality to one instance of a class.
  • Class Method: Provides functionality to a class itself