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