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Vicki Langer
Vicki Langer

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Ruby Self & Attr, as a Python Dev

#ruby #codenewbie #python

This is a continuation of Picking up Ruby Fast, as a Python Dev. Again, expect examples with pets and minimal math

What is self

self is a method called on the class itself. It can be done in a couple of different ways. The first is similar to Python. The second with the << is new to me.

In these examples, I'm just gonna add 1 to a count of how many dog or cat instances we've created.

self.

words

class Dog @@num_dogs = 0 def initialize @@num_dogs += 1 end def self.num_monkeys @@num_dogs end end # to get the num of dogs self.num_dogs
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class << self

In this example, the class << self is saying that everything before the end is a class method and is not for the instances.

class Cat @@num_cats = 0 def initialize @@num_cats += 1 end class << self def num_cats @@num_cats end end end # to get the num of cats Cat.num_cats
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attr

We can use the following to easily read, write, and grab attributes of a class: attr_reader, attr_writer, and attr_accessor. They all automatically create methods that do things to keep us from having to write so many methods.

Giving a symbol to attr_reader automatically makes a method by the name of the symbol that will read the instance variable by the same name.

attr_writer will automatically create a method ending with an = with will then write/set the symbol's instance variable to the value given.

attr_accessor is the best of both worlds and it automatically creates methods to read and write. Again, it uses the name of the symbol given.

The example below shows a Kitty class with these different attr things.

class Kitty attr_accessor :name # creates method to read/get & write/set the instance variable attr_reader :lives_remaining # creates method to read/get the instance variable def initialize name @name = name @lives_remaining = 9 end end # irb and output irb(main):003:0> cat_1 = Kitty.new('Mouse') => #<Kitty:0x00007fa04e956f50 @name="Mouse", @lives_remaining=9>
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More New Stuff that I Never Saw in Python

Every time I see something new-to-me in Ruby I wonder if it's because I never came across it in Python or because Ruby just has all sort of cool stuff that Python doesn't have.

method_name=

Turns out method names can not only end with question marks, but they can also end with equal signs.

Ending a method with an =, Ruby reads it as "this method is going to change the value of something"

In this example, we have a Cat class. We're going to create a new cat. Then, we are going to rename that cat.

class Cat def initialize name @name = name end def name= new_name @name = new_name end end # output irb(main):005:0> cat_one = Cat.new 'Blocks' irb(main):012:0> cat_one => #<Cat:0x00007ff6948b19a0 @name="Blocks"> irb(main):013:0> cat_one.name = "Socks" => "Socks" irb(main):014:0> cat_one => #<Cat:0x00007ff6948b19a0 @name="Socks">
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Reminder To Self (haha, get it :D)

  1. Use irb in terminal to get IRB. I keep getting this mixed up because Python uses python to get REPL.

If you missed the first post in this series, I've heard it's a good read and there's cats.

vickilanger

Picking up Ruby Fast, as a Python Dev

Vicki Langer ・ Nov 12 '20

#ruby #python #codenewbie

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