468 lines
11 KiB
Markdown
468 lines
11 KiB
Markdown
# Ruby Cheatsheet
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##### Table of Contents
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- [Basics](#basics)
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- [Vars, Constants, Arrays, Hashes & Symbols](#vars-constants-arrays-hashes--symbols)
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- [Methods](#methods)
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- [Classes](#classes)
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- [Modules](#modules)
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- [Blocks & Procs](#blocks--procs)
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- [Lambdas](#lambdas)
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- [Calculation](#calculation)
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- [Commenting](#commenting)
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- [Conditions](#conditions)
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- [Printing & Putting](#printing--putting)
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- [User Input](#user-input)
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- [Loops](#loops)
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- [Sorting & Comparing](#sorting--comparing)
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- [Useful Methods](#useful-methods)
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## Basics
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- `$ irb`: to write ruby in the terminal
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- don't use `'` in ruby, use `"` instead
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- you can replace most `{}` with `do end` and vice versa –– not true for hashes or `#{}` escapings
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- Best Practice: end names that produce booleans with question mark
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- CRUD: create, read, update, delete
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- `[1,2].map(&:to_i)`
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- `integer`: number without decimal
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- `float`: number with decimal
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- tag your variables:
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- - `$`: global variable
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- - `@`: instance variable
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- - `@@`: class variable
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- `1_000_000`: 1000000 –– just easier to read\*
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## Vars, Constants, Arrays, Hashes & Symbols
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```Ruby
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my_variable = “Hello”
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my_variable.capitalize! # ! changes the value of the var same as my_name = my_name.capitalize
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my_variable ||= "Hi" # ||= is a conditional assignment only set the variable if it was not set before.
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```
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### Constants
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```Ruby
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MY_CONSTANT = # something
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```
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### Arrays
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```Ruby
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my_array = [a,b,c,d,e]
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my_array[1] # b
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my_array[2..-1] # c , d , e
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multi_d = [[0,1],[0,1]]
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[1, 2, 3] << 4 # [1, 2, 3, 4] same as [1, 2, 3].push(4)
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```
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### Hashes
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```Ruby
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hash = { "key1" => "value1", "key2" => "value2" } # same as objects in JavaScript
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hash = { key1: "value1", key2: "value2" } # the same hash using symbols instead of strings
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my_hash = Hash.new # same as my_hash = {} – set a new key like so: pets["Stevie"] = "cat"
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pets["key1"] # value1
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pets["Stevie"] # cat
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my_hash = Hash.new("default value")
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hash.select{ |key, value| value > 3 } # selects all keys in hash that have a value greater than 3
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hash.each_key { |k| print k, " " } # ==> key1 key2
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hash.each_value { |v| print v } # ==> value1value2
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my_hash.each_value { |v| print v, " " }
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# ==> 1 2 3
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```
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### Symbols
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```Ruby
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:symbol # symbol is like an ID in html. :symbol != "symbol"
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# Symbols are often used as Hash keys or referencing method names.
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# They can not be changed once created. They save memory (only one copy at a given time). Faster.
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:test.to_s # converts to "test"
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"test".to_sym # converts to :test
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"test".intern # :test
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# Symbols can be used like this as well:
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my_hash = { key: "value", key2: "value" } # is equal to { :key => "value", :key2 => "value" }
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```
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#### Functions to create Arrays
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```Ruby
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"bla,bla".split(“,”) # takes string and returns an array (here ["bla","bla"])
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```
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## Methods
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**Methods**
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```Ruby
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def greeting(hello, *names) # *names is a split argument, takes several parameters passed in an array
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return "#{hello}, #{names}"
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end
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start = greeting("Hi", "Justin", "Maria", "Herbert") # call a method by name
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def name(variable=default)
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### The last line in here gets returned by default
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end
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```
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## Classes
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_custom objects_
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```Ruby
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class Person # class names are rather written in PascalCase (It is similar to camelCase, but the first letter is capitalized)
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@@count = 0
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attr_reader :name # make it readable
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attr_writer :name # make it writable
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attr_accessor :name # makes it readable and writable
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def Methodname(parameter)
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@classVariable = parameter
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@@count += 1
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end
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def self.show_classVariable
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@classVariable
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end
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def Person.get_counts # is a class method
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return @@count
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end
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private
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def private_method; end # Private methods go here
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end
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matz = Person.new("Yukihiro")
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matz.show_name # Yukihiro
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```
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### Inheritance
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```Ruby
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class DerivedClass < BaseClass; end # if you want to end a Ruby statement without going to a new line, you can just type a semicolon.
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class DerivedClass < Base
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def some_method
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super(optional args) # When you call super from inside a method, that tells Ruby to look in the superclass of the current class and find a method with the same name as the one from which super is called. If it finds it, Ruby will use the superclass' version of the method.
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# Some stuff
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end
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end
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end
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# Any given Ruby class can have only one superclass. Use mixins if you want to incorporate data or behavior from several classes into a single class.
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```
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## Modules
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```Ruby
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module ModuleName # module names are rather written in PascalCase
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# variables in modules doesn't make much sence since modules do not change. Use constants.
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end
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Math::PI # using PI constant from Math module. Double colon = scope resolution operator = tells Ruby where you're looking for a specific bit of code.
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require 'date' # to use external modules.
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puts Date.today # 2016-03-18
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module Action
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def jump
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@distance = rand(4) + 2
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puts "I jumped forward #{@distance} feet!"
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end
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end
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class Rabbit
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include Action # Any class that includes a certain module can use those module's methods! This now is called a Mixin.
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extend Action # extend keyword mixes a module's methods at the class level. This means that class itself can use the methods, as opposed to instances of the class.
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attr_reader :name
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def initialize(name)
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@name = name
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end
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end
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peter = Rabbit.new("Peter")
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peter.jump # include
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Rabbit.jump # extend
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```
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## Blocks & Procs
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### Code Blocks
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_Blocks are not objects._ A block is just a bit of code between do..end or {}. It's not an object on its own, but it can be passed to methods like .each or .select.
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```Ruby
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def yield_name(name)
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yield("Kim") # print "My name is Kim. "
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yield(name) # print "My name is Eric. "
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end
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yield_name("Eric") { |n| print "My name is #{n}. " } # My name is Kim. My name is Eric.
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yield_name("Peter") { |n| print "My name is #{n}. " } # My name is Kim. My name is Eric. My name is Kim. My name is Peter.
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```
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### Proc
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_Saves blocks and are objects._ A proc is a saved block we can use over and over.
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```Ruby
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cube = Proc.new { |x| x ** 3 }
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[1, 2, 3].collect!(&cube) # [1, 8, 27] # the & is needed to transform the Proc to a block.
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cube.call # call procs directly
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```
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## Lambdas
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```Ruby
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lambda { |param| block }
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multiply = lambda { |x| x * 3 }
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y = [1, 2].collect(&multiply) # 3 , 6
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```
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Diff between procs and lambdas:
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- a lambda checks the number of arguments passed to it, while a proc does not (This means that a lambda will throw an error if you pass it the wrong number of arguments, whereas a proc will ignore unexpected arguments and assign nil to any that are missing.)
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- when a lambda returns, it passes control back to the calling method; when a proc returns, it does so immediately, without going back to the calling method.
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So: A lambda is just like a proc, only it cares about the number of arguments it gets and it returns to its calling method rather than returning immediately.
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## Calculation
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- Addition (+)
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- Subtraction (-)
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- Multiplication (\*)
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- Division (/)
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- Exponentiation (\*\*)
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- Modulo (%)
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- The concatenation operator (<<)
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- you can do 1 += 1 –– which gives you 2 but 1++ and 1-- does not exist in ruby
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- `"A " << "B"` => `"A B"` but `"A " + "B"` would work as well but `"A " + 4 + " B"` not. So rather use string interpolation (`#{4}`)
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- `"A #{4} B"` => `"A 4 B"`
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## Commenting
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```Ruby
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=begin
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Bla
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Multyline comment
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=end
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```
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```Ruby
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# single line comment
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```
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## Conditions
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### If
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```Ruby
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if 1 < 2
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puts “one smaller than two”
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elsif 1 > 2 # *careful not to mistake with else if. In ruby you write elsif*
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puts “elsif”
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else
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puts “false”
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end
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# or
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puts "be printed" if true
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puts 3 > 4 ? "if true" : "else" # else will be putted
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```
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### Unless
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```Ruby
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unless false # unless checks if the statement is false (opposite to if).
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puts “I’m here”
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else
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puts “not here”
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end
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# or
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puts "not printed" unless true
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```
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### Case
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```Ruby
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case my_var
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when "some value"
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###
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when "some other value"
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###
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else
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###
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end
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# or
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case my_var
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when "some value" then ###
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when "some other value" then ###
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else ###
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end
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```
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- `&&`: and
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- `||`: or
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- `!`: not
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- `(x && (y || w)) && z`: use parenthesis to combine arguments
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- problem = false
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- print "Good to go!" unless problem –– prints out because problem != true
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## Printing & Putting
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```Ruby
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print "bla"
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puts "test" # puts the text in a separate line
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```
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## String Methods
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```Ruby
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"Hello".length # 5
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"Hello".reverse # “olleH”
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"Hello".upcase # “HELLO”
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"Hello".downcase # “hello”
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"hello".capitalize # “Hello”
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"Hello".include? "i" # equals to false because there is no i in Hello
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"Hello".gsub!(/e/, "o") # Hollo
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"1".to_i # transform string to integer –– 1
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"test".to_sym # converts to :test
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"test".intern # :test
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:test.to_s # converts to "test"
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```
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## User Input
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```Ruby
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gets # is the Ruby equivalent to prompt in javascript (method that gets input from the user)
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gets.chomp # removes extra line created after gets (usually used like this)
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```
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## Loops
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### While loop
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```Ruby
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i = 1
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while i < 11
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puts i
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i = i + 1
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end
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```
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### Until loop
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```Ruby
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i = 0
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until i == 6
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puts i
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i += 1
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end
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```
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### For loop
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```Ruby
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for i in 1...10 # ... tells ruby to exclude the last number (here 10 if we .. only then it includes the last num)
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puts i
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end
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```
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### Loop iterator
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```Ruby
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i = 0
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loop do
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i += 1
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print "I'm currently number #{i}” # a way to have ruby code in a string
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break if i > 5
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end
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```
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### Next
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```Ruby
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for i in 1..5
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next if i % 2 == 0 # If the remainder of i / 2 is zero, we go to the next iteration of the loop.
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print i
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end
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```
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### .each
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```Ruby
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things.each do |item| # for each things in things do something while storing that things in the variable item
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print “#{item}"
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end
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```
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on hashes like so:
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```Ruby
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hashes.each do |x,y|
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print "#{x}: #{y}"
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end
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```
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### .times
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```Ruby
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10.times do
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print “this text will appear 10 times”
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end
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```
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### .upto / .downto
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```Ruby
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10.upto(15) { |x| print x, " " } # 10 11 12 13 14 15
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"a".upto("c") { |x| print x, " " } # a b c
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```
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## Sorting & Comparing
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```Ruby
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array = [5,4,1,3,2]
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array.sort! # = [1,2,3,4,5] – works with text and other as well.
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"b" <=> "a" # = 1 – combined comparison operator. Returns 0 if first = second, 1 if first > second, -1 if first < second
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array.sort! { |a, b| b <=> a } # to sort from Z to A instead of A to Z
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```
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## Useful Methods
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```Ruby
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1.is_a? Integer # returns true
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:1.is_a? Symbol # returns true
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"1".is_a? String # returns true
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[1,2,3].collect!() # does something to every element (overwrites original with ! mark)
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.map() # is the same as .collect
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1.2.floor # 1 # rounds a float (a number with a decimal) down to the nearest integer.
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cube.call # implying that cube is a proc, call calls procs directly
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Time.now # displays the actual time
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``` |