Module, mixins and file handling in ruby

Module
By Ananta Raj lamichhane

Module
Module are wrapper around the ruby code.
Module cannot be instantiated.
Module are used in conjunction with the
classes.

Modules: namespaces
bundle logically related object together.
identifies a set of names when objects having different
origins but the same names are mixed together.
-so that there is no ambiguity.

Example
Class Date
…....
end
dinner= Date.new
dinner.date= Date.new
Conflict!!!
Module Romantic
Class Date
…....
end
end
dinner= Romantic::Date.new
dinner.date= Date.new
:: is a constant lookup operator

Namespace can:
Keep class name distinct from another ruby class.
Ensure classes used in open source won't conflict.

Module:Mix-ins
Ruby doesn't let us have multiple inheritance.
For additional functionality-
place into a module and mixed it in to any class that needs
it.
Powerful way to keep the code organize.

Example
class Person
attr_accessor :first_name, :last_name, :city,
:state
def full_name
@first_name + " " + @last_name
end
end
class Teacher
end
class Student
end

module ContactInfo
attr_accessor :first_name, :last_name, :city, :state
def full_name
@first_name + " " + @last_name
end
end

…...person.rb…….
require 'contact_info'
class Person
include ContactInfo
end
….teacher.rb………...
class Teacher
include ContactInfo
end
...student.rb…………..
class Student
include ContactInfo
end
2.1.1 :002 > t= Teacher.new
=> #<Teacher:0x00000004576198>
2.1.1 :003 > t.first_name="tfn"
=> "tfn"
2.1.1 :004 > t.last_name="tln"
=> "tln"
2.1.1 :005 > t.full_name
=> "tfn tln"
2.1.1 :006 > p= Person.new
=> #<Person:0x0000000454b5b0>
2.1.1 :007 > p.first_name="pfn"
=> "pfn"
2.1.1 :008 > p.last_name="pln"
=> "pln"
2.1.1 :009 > p.full_name
=> "pfn pln"
2.1.1 :010 >

OR
class student < Person
attr_accesor :books
end

Modules are usually kept in separate file.
Need to have a way to load modules into ruby.

include:
use module as maxin.
has nothing to do with loading the files
load:
load the file everytime we call. hence return true on every call
use when you want to refresh the code and one to call the second time.
disadvantage
Once ruby sees the file, there is no reason to call it again.
The code in load execute every time we call it .
require:
Keep track of the fact that is included.
only include if it has not been loaded before.
load source file only once.

Modules:Enumerable as Mixin
provides a number of methods for objects which are
iterable collection of other objects, like arrays, ranges or
hashes.
ex: sort, reject, detect, select, collect, inject
They may have slightly different behaviour in each one but are the same functionality.
must provide method each,-yields every member of the
collection one-by-one.
each-takes the block of code and iterates all the object of
the collection, passing it to the given block.

http://www.ruby-doc.org/core-2.2.0/Array.html
http://www.ruby-doc.org/core-2.2.0/Hash.html
http://www.ruby-doc.org/core-2.2.0/Range.html

class ToDoList
include Enumerable
attr_accessor :items
def initialize
@items = []
end
def each
@items.each {|item| yield item}
end
end
2.1.1 :006 > load 'to_do_list.rb'
=> true
2.1.1 :007 > tdl= ToDoList.new
=> #<ToDoList:0x000000028d12b8 @items=[]>
2.1.1 :009 > tdl.items= ["aaaa","bbbbbbbb","ddddddd"]
=> ["aaaa", "bbbbbbbb", "ddddddd"]
2.1.1 :011 > tdl.select {|i| i.length >4}
=> ["bbbbbbbb", "ddddddd"]

compare the objects- if they are equal, less or greater than other, and to sort
the collection of such objects.
The class must define the <=> (Spaceship) operator, which compares the
receiver against another object,
Ruby built-in object, like Fixnum or String, use this mixin to provide comparing
operator.
returns -1 if the left object is greater than the right one, 0 when they are equal
and 1 in case the right is greater then the left

Example
class Server
attr_reader :name, :no_processors, :memory_gb # we must provide readers to
this attributes
include Comparable # because we are comparing the other
Server with self
def initialize(name, no_processors, memory_gb)
@name = name
@no_processors = no_processors
@memory_gb = memory_gb
end
# def inspect
# "/Server: #{@name}: #{@no_processors} procs, #{@memory_gb} GiB mem/"
# end
def <=>(other)
if self.no_processors == other.no_processors # if there is the
same number of procs
self.memory_gb <=> other.memory_gb #
comparing memory
else
self.no_processors <=> other.no_processors # otherwise
comparing the number of processors
end
endend

Class work
Class Assignment : Write a class Animal with attributes name and
scientific_name. Write a class Human with attributes first_name, last_name and
scientific_name. Write a mixin called Name which has a method
complete_name. Include this mixin in both Animal and Human class.
The method should return “name(scientific_name)” for animals e.g. Frog(Rana
Tigrina). For Human it should return “first_name last_name(scientific name)”
e.g. John Doe(Homo Sapiens)

Input/Output basic
Input: -> into a ruby program.
Basic ruby inputs
gets
Output:-> from that program.
Basic ruby outputs
puts
print

Introduction
File represents digital information that exists on durable storage.
In Ruby File<IO
File is just a type of input and output.
Read from the file-> input
Write to the file->output

Writing(output) to files
file= File.new(‘test.txt’, ‘w’)
‘W’: Write-only, truncates existing file
to zero length or creates a new file for writing
file.puts “abcd”
file.close
OR
file.prints “efgh” or
file.writes “ijkl”- returns number of character that it wrote.
file << “mnop”

Reading(Input) from files
file= File.new(‘test.txt’, ‘r’)
"r" Read-only, starts at beginning of file (default mode)
file.gets
=> "uvwx"
Note: puts vs gets
file.gets -> get next line.
file.read(4): takes in how many character to read
file.close.

Opening files
We open an existing file using
File.open(“test.txt”, ‘r’).
We will pass the file name and a second
argument which will decide how the file will be
opened.
Open File For Reading
Reading file contents is easy in Ruby. Here are two options:
File.read("file_name") - Spits out entire contents of the file.
File.readlines("file_name") - Reads the entire file based on
individual lines and returns those lines in an array.

"r" Read-only, starts at beginning of file
(default mode).
"r+" Read-write, starts at beginning of file.
"w" Write-only, truncates existing file
to zero length or creates a new file
for writing.
"w+" Read-write, truncates existing file to zero
length
or creates a new file for reading and
writing.
"a" Write-only, starts at end of file if file exists,
otherwise creates a new file for
writing.
"a+" Read-write, starts at end of file if file exists,
otherwise creates a new file for
reading and
writing.

Open File For Writing
We can use write or puts to write files.
Difference
puts- adds a line break to the end of strings
write- does not.
File.open("simple_file.txt", "w") { |file|
file.write("adding first line of text") }
Note: the file closes at the end of the block.

Other examples:
2.1.1 :017 > File.read('simple_file1.txt')
=> "adding first line of text"
2.1.1 :018 > File.open('simple_file1.txt','a+') do |file|
2.1.1 :019 > file.write('writing to the file1')
2.1.1 :020?> end
=> 20
=> "adding first line of textwriting to the file1"
2.1.1 :022 > File.open('simple_file1.txt','w+') do |file|
2.1.1 :023 > file.write('where m i ')
2.1.1 :024?> end
=> 10
=> "where m i "

Deleting a file
irb :001 > File.new("dummy_file.txt", "w+")
=> #<File:dummy_file.txt>
irb :002 > File.delete("dummy_file.txt")
=> 1

Assignments
Day 4
Class Assignment 1: Write a module named MyFileModule. It should following methods:
a. create_file(path)
b. edit_file(path,content)
c. delete_file(path)
Necessary exception handling should be done.
Class Assignment 2: Write a class Animal with attributes name and scientific_name. Write a class Human with attributes
first_name, last_name and scientific_name. Write a mixin called Name which has a method complete_name. Include this mixin in
both Animal and Human class.
The method should return “name(scientific_name)” for animals e.g. Frog(Rana Tigrina). For Human it should return “first_name
last_name(scientific name)” e.g. John Doe(Homo Sapiens)
1. Write a program to adjust time in a movie subtitle. The input to the program should be path to the subtitle file and adjust time in
seconds (positive value to increase and negative value to decrease time). The program then creates a new subtitle file with
adjusted time without changing.

Module, mixins and file handling in ruby

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