Ruby Totorial

BackEnd Ruby

创建时间:2020-02-09 13:22

字数:1.6k 阅读:

1. Basics

Met circumstances where need Ruby knowledge to resolve problems, thus need to do a quick touch on Ruby, at least know how to read ruby code.

Leran by doing, or we say, learn by satisfying current needs.

1. Basics

features
- object-oriented
- server side scripting language
- can be used to write common gateway interface(CGI) scripts

1.1 Syntax of Ruby

whitespace
- ignored in ruby code, except when they appear in strings.
end of line
- you could use
  - semicolons
  - newline characters as the ending of a statement
Ruby Identifiers
- case sensitive
comments
- #
- =begin at beginning, =end at the end

// Declares code to be called before the program run 
BEGIN {
    code
}

// Declares code to be called at the end of the program 
END {
    code
}

classes and objects
- features
  - data encapsulation
  - data abstraction
  - polymorphism
  - inheritance

// Class example
Class Vehicle {

   Number no_of_wheels
   Number horsepower
   Characters type_of_tank
   Number Capacity
   Function speeding {
   }

   Function driving {
   }

   Function halting {
   }
}

1.2 Class and Objects

Define a class in Ruby

// A class always starts with keyword class, followed by the name of the class. 
// Terminate a class by using the keyword end. 
class Customer
end

Variables in a Ruby Class
- local variables
  - defined in a method
  - begin with a lowercase letter or _.
- instance variables
  - available across methods for any particular instance or object
  - instance variables change from object to object
  - @
- class variables
  - available across different objects
  - belongs to the class and is a characteristic of a class
  - @@
- global variables
  - Class variables are not available across classes, while global variables are.
  - $

// Determine the number of objects that are being ccreated 
class Customer
   @@no_of_customers = 0
end

creating objects with new method
- object1 = Customer.new
- object1 is object name
- Customer is class
- To instantiate a new object, you need to use class name followed by dot and new(keyword)
custom method to create ruby objects (similar to constructor concept in Java)
- pass parameters to method new
- when you plan to declare new method with parameters, you need to declare the method initialize at the time of the class creation

class Customer
   @@no_of_customers = 0
   def initialize(id, name, addr)
      @cust_id = id
      @cust_name = name
      @cust_addr = addr
   end
end

// To create objects 
cust1 = Customer.new("1", "John", "Wisdom Apartments, Ludhiya")

member functions in class
- each method in a class starts with the keyword def followed by the method name

class Sample
    def function
        statement 1
        statement 2
    end
end



// A full example 
#!/usr/bin/ruby
class Sample
   def hello
      puts "Hello Ruby!"
   end
end

# Now using above class to create objects
object = Sample. new
object.hello

1.3 Variables

Global Variables
- begin with $
- uninitialized global variables have the value nil

#!/usr/bin/ruby

$global_variable = 10
class Class1
   def print_global
      # In ruby, you can use HashTag to access any variables value 
      puts "Global variable in Class1 is #$global_variable"
   end
end
class Class2
   def print_global
      puts "Global variable in Class2 is #$global_variable"
   end
end

class1obj = Class1.new
class1obj.print_global
class2obj = Class2.new
class2obj.print_global

Instance Variables
- begin with @

#!/usr/bin/ruby

class Customer
   def initialize(id, name, addr)
      @cust_id = id
      @cust_name = name
      @cust_addr = addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
   end
end

# Create Objects
cust1 = Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2 = Customer.new("2", "Poul", "New Empire road, Khandala")

# Call Methods
cust1.display_details()
cust2.display_details()

Class Variables
- begin with @@
- must be initialized before they can be used in method definitions

#!/usr/bin/ruby

class Customer
   @@no_of_customers = 0
   def initialize(id, name, addr)
      @cust_id = id
      @cust_name = name
      @cust_addr = addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
   end
   def total_no_of_customers()
      @@no_of_customers += 1
      puts "Total number of customers: #@@no_of_customers"
   end
end

# Create Objects
cust1 = Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2 = Customer.new("2", "Poul", "New Empire road, Khandala")

# Call Methods
cust1.total_no_of_customers()
cust2.total_no_of_customers()

Local variables
- begin with a lowercase letter or _
- scope
  - class
  - module
  - def
  - do to the corresponding end
  - block’s opening brace to its close brace
Constants
- Begin with an uppercase letter
- defined within a class or module
Pseudo-variables
- self
- true
- false
- nil
  - Value representing undefined
- _FILE_
  - the name of the current source file
- _LINE_
  - the current line number in the source file
    1.4 Arrays
    Array are created by placing a comma-separated series of object references between the square brackets.
  #!/usr/bin/ruby
  
  ary = [ “fred”, 10, 3.14, “This is a string”, “last element”, ]
  ary.each do |i|
  puts i
  end

1.5 Hashes

Hash is created by placing a list of key/value pairs between braces, with either a comma or the sequence => between the key and the value. A trailing comma is ignored.

#!/usr/bin/ruby

hsh = colors = { "red" => 0xf00, "green" => 0x0f0, "blue" => 0x00f }
hsh.each do |key, value|
   print key, " is ", value, "\n"
end

1.6 Ranges

A Range represents an interval which is a set of values with a start and an end. Ranges may be constructed using the s..e and s…e literals, or with Range.new.

#!/usr/bin/ruby

(10..15).each do |n| 
   print n, ' ' 
end

1.7 Operators

<=>
- ruturn 0 if first operand equals second
- 1 if first greater than second
- -1 if first less than second
.eql?
- true if the receiver and argument have both the same type and equal values
equal?
- true if the receiver and argument have the same object id
..
- 1..10 creates a range from 1 to 10 inclusive
...
- 1…10 creates a range from 1 to 9
defined? operators
- takes the form of a method call to determine whether or not the passed expression is defined
- returns a description string of the expression, or nil if the expression isn’t defined
dot operators
double colon :: operators
- You call a module method by preceding its name with the module’s name and a period, and you reference a constant using the module name and two colons.
- :: us a unary operator that allows constants, instance methods and class methods defined within a class or module to be accessed from anywhere outside the class or module
- *Classes and methods are considered to be constants too *

1.8 Conditions

// if else condition check
if condition
    code..
elsif condition2
    code
else 
    code
end

// case 
#!/usr/bin/ruby

$age =  5
case $age
when 0 .. 2
   puts "baby"
when 3 .. 6
   puts "little child"
when 7 .. 12
   puts "child"
when 13 .. 18
   puts "youth"
else
   puts "adult"
end

1.9 Loops

while condition do 
    code
end

Executes code while conditional is true

$i = 0
$num = 5
begin 
    puts("123")
    $i += 1
end while $i < $num 

// for loop
for i in 0..5
    puts "Value of local variable is #{i}"
end

// subtitute way of for loop
(expression).each do |variable| 
    code
end

// E.G 
(0..5).each do |i|
    puts "Value of local variable is #{i}"
end

next
- jump to the next iteration of the most internal loop
redo
- restarts this iteration of the most internal loop, without checking loop condition
retry
break
- terminate the most internal loop

1.10 Methods

used to bundle one or more repeatable statements into a single unit
method name should begin with a lowercase lettter
method should be defined before calling them
call the method by direcly type in the method name method_name
with parameters method_name 25, 30
Ruby will return the value of lat statement by default
or use the return statement
method defined in the class definition are marked as public by default
a block is always invoked from a function with the same name as that of the block

def method_name (var1, var2)
```
  expr
```
end
variable number of parameters
- def sample (*test)

1.11 Blocks

definition
- consists of chunks of code
- assign a name to a block
- code in the block is always enclosed within braces {} or ()
- a block is always invoked from a function with the same name as that of the block
- invoke a block by using the yield statement
if the last argument of a method is preceded by &, then you can pass a block to this method and this block will be assigned to the last parameter.

#!/usr/bin/ruby

def test(&block)
   block.call
end
test { puts "Hello World!"}

1.12 Modules and Mixins

Module
- way of grouping together methods, classes, and constants
- provides namespace and prevent name clashes
  - a sandbox
- implement mixin facility

// syntax
module Identifier
    statement1
    statement2
end

call a module method by precedint its name with the module’s name and a period
reference a constant using the module name and two colons

#!/usr/bin/ruby

# Module defined in trig.rb file

module Trig
   PI = 3.141592654
   def Trig.sin(x)
   # ..
   end
   def Trig.cos(x)
   # ..
   end
end

require
- similar to import, include
- if a third program wants to use any defined module, it can simply load the module files using the Rubyrequire statement
mixin
- multiple inheratance

module A
   def a1
   end
   def a2
   end
end
module B
   def b1
   end
   def b2
   end
end

class Sample
include A
include B
   def s1
   end
end

samp = Sample.new
samp.a1
samp.a2
samp.b1
samp.b2
samp.s1

In this way, samp could call method defined in Module A and Module B

1.13 Strings

holds and manipulates an arbitrary sequence of one or more bytes

1.14 Array

ordered, integer indexed collections of any object
each element in an array is associated with and referred to by an index
creating arrays
- Array.new

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