Tips: Ruby on Rails

Different ways to print

• p: for debugging. For each object, directly writes obj.inspect followed by a newline
• print: low level, does not add new line or separator by default
• puts: like regular print in other languages

Array methods

Method Name Aliases

• Array#filter === Array#select
• Array#map === Array#collect
• Array#member? === Array.include?

Slicing

• Array#to return the beginning of the array up to position (inclusive)
• Array#from return the tail of the array from position (inclusive)
• Hash#slice select keys from a hash

Iterator

• Array#each
• Hash#each
• .map.with_index
  • For example: 'abcd'.map.with_index {|x, i| x * i} #=> ["", "b", "cc", "ddd"]

Empty/Nil/Blank/etc

• #empty?
  • Ruby method; exists on Array, Set, Hash, String
  • does not exist on all Enumerable
  • on string: true iff it's empty string
• #nil?
  • Ruby method; exists on Object class
  • true iff it's nil
• #blank?
  • Rails ActiveSupport method
  • on string: true iff the string is whitespace only
  • on array/set/hash: same as #empty?
  • true is not blank, nil & false are blank
• #present?
  • opposite of #blank?
• #presence
  • return self if present, else nil

See also:

• if obj.present? vs if obj
• Rails ActiveSupport source code
• Differences Between #nil?, #empty?, #blank?, and #present?

Different ways to update a record

Source

hash literal punning

ruby shorthand hash syntax (punning in js) (ruby 3.1+)

a = 1
b = 2

{ a:, b: }
# => { a: 1, b: 2 }

string/symbol as hash keys

    {  abc:    "key is a symbol" }
=== {  :abc => "key is a symbol" }
=== { "abc":   "key is a symbol" }

!== { "abc" => "key is a string" }

Mandatory method keyword arguments

#You must name the keyword arg when calling this function
def action(amount:, reason: 'default value')
  @amount = amount
  @reason = reason
end

Variables that starting with @

Class variable scoping

• @@xxx class variable
• @xxx instance variable

meta programming

a = {}
# Get information of available functions
a.methods
a.method(:to_json)
a.method(:to_json).arity  # get expected # of args

# Call a function
   a.send(:slice, :key1, :key2)
== a.method(:slice).call(:key1, :key2)

# list all methods that ends with '?'
'abc'.methods.filter { |a| a.to_s.ends_with?('?') }

attr_accessor

• attr_accessor can read and write
• attr_reader only read value
• attr_writer only assign value

https://www.rubyguides.com/2018/11/attr_accessor/

We want expose internal value to outside world

class Food
  def initialize(protein)
    @protein = protein
  end
end
bacon = Food.new(21)

# You can define the following methods:
  def protein
    @protein
  end

  def protein=(value)
    @protein = value
  end

# OR simply have:
class Food
	attr_accessor :protein
  ...
end

class static method syntax

class A
	class << self
		def method
	    	...
		end
	end
end

is equivalent to

class A
	def self.method
		...
	end
end