This is a continuation of Picking up Ruby Fast, as a Python Dev. Again, expect examples with minimal math
Everything is an object and there are so many different kinds of variables! Every day I look at Ruby I learn new things. I'm really enjoying it.
Objectification
Data Types == Instances of Classes
Each data type was created by a class. I guess this is probably the same in Python and other languages, but it's definitely not something I've thought about. So, somewhere there is a class that says what an int is. This feels very existential. It reminds me of this question I got from a student last month:
How did we program an editor to write programs if we didn't have a program to program programs?
Anyway, we can use the .class method to find out what each item is.
irb(main):189:0> 1.class => Integer irb(main):190:0> 34.6.class => Float irb(main):191:0> "Mouse".class => String The same works for variables.
irb(main):192:0> cat = 78 => 78 irb(main):193:0> cat.class => Integer irb(main):194:0> dog = "Wiley" => "Wiley" irb(main):195:0> dog.class => String Variable Types
Turns out, Ruby has 4 types of variables. Who knew? Okay, I'm sure lots of people did, but I didn't.
local
These are variables that are likely to be used quickly. If created outside of a class, method, or block they cannot be pulled into a method or anywhere else for that matter. Most of the examples I've had were using local variables.
The iterator variables used in blocks are also local variables as they can't be used after the end of the block.
global
Global variables start with $. These variables can be created outside of a method, in a class, or anywhere and then it can be used anywhere.
Here's global variable that we are going to send to the method greet:
$language = "Ruby" # hey look, a global var def greet puts "we're learning " + $language end # running & output irb(main):218:0> greet we're learning Ruby class
Class variables start with @@. These variables can be used inside the class and by all instances of the class. These are for classes to save info about themselves. It seems these aren't used very often. Class variables are limited in usefulness because all instances of the class share that one variable.
class Player @@moves = 9 def initialize(name, letter='x') @name = name @letter = letter end def mark_spot letter if @@moves > 0 @@moves -= 1 puts "drew an #{letter}! Moves left: #{@@moves}" else puts 'no more spells' end end end # running & output irb(main):231:0> wiley = Player.new("Wiley", "x") => #<Player:0x00007fcee80dd838 @name="Wiley", @letter="x"> irb(main):232:0> cheeto = Player.new("Cheeto", "o") => #<Player:0x00007fcee8101cd8 @name="Cheeto", @letter="o"> irb(main):235:0> wiley.mark_spot "x" drew an x! Moves left: 8 => nil irb(main):236:0> cheeto.mark_spot "o" drew an o! Moves left: 7 => nil The problem here is that both players are sharing the @@moves. It may work in this example, but it often won't.
instance
Instance variables start with @. Instance variables are seen inside the class and by all instances of the class. However, each instance of a class gets its very own copy of the variable. Each instance doesn't have to share with other instances.
In the class variable, I gave a total number of moves, but in reality, most games allow each person to take the same amount of move. So, player1 would have 5 moves and player2 would have 5 moves. Then, we'd go until the game ends. We wouldn't typically share a pool of movies.
class Player def initialize(name, letter='x') @name = name @letter = letter @moves = 5 end def mark_spot letter if @moves > 0 @moves -= 1 puts "drew an #{letter}! Moves left: #{@moves}" else puts 'no more spells' end end end # running & output irb(main):239:0> remmy = Player.new "Remmy", 'x' => #<Player:0x00007fcee40f9780 @name="Remmy", @letter="x", @moves=5> irb(main):240:0> puppy = Player.new "Puppy", 'o' => #<Player:0x00007fcee4100058 @name="Puppy", @letter="o", @moves=5> irb(main):241:0> puppy.mark_spot 'o' drew an o! Moves left: 4 => nil irb(main):242:0> remmy.mark_spot 'x' drew an x! Moves left: 4 => nil irb(main):243:0> puppy.mark_spot 'o' drew an o! Moves left: 3 => nil This works much better because now each player has their own set of moves.
If you missed the first post in this series, I've heard it's a good read and there's cats.
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