effetive-ruby-tldr-part2

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#11. Create namespace by nesting code in Module

  • Use modules to create namespece by nesting definiton inside them.
  • Mirror you namesapece structure to your dir structure.
  • Use :: to fully qualify a top-level constant.

#12. Understand the Different Flavors of Equality

  • Use == to test if two obejcts represent the same value.
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1 == `1.0` # true
  • Use eql? to test if two objects represent the same value and also the same
    type.
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1 == `1.0` # false
1 == 1 # true

  • Use equal? to test if two objects are the same object (with same object_id),
    so never override this method.

  • === - == || =~ || is_a?

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'a'==='a' #true -  'a'=='a'
/a/i==='Abc' #0 - /a/i =~ 'Abc'
String==='a' #true - 'a'.is_a? String

#13. Implement Comparison via <=> and the Comparable Module

  • Implement object ordering by defining a “<=>” operator and including the Comparable module.
  • The “<=>” operator should return nil if the left operand can’t be compared with the right.
  • If you implement “<=>” for a class you should consider aliasing eql? to “==”, especially if you want instances to be usable as hash keys. In which case you should also override the hash method. NOTE. == does NOT test type equity.

#14. Share Private State Through Protected Methods

  • Protected methods can be called with an explicit receiver from objects of the same class

#15. Prefer Class Instance Variables to Class Variables

#16. Duplicate Collections Passed as Arguments Before Mutating Them

  • Method arguments in Ruby are passed as references, not values
  • The dup and clone methods only create shallow copies.
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class User
  attr_accessor :name

  def initialize(name)
    @name = name
  end
end

u1 = User.new 'kevin'
u2 = Use.new 'others'

arr = [u1, u2]
arr2 = arr.dup

u2.name = 'new name'

arr == arr2 # true
  • For most objects, Marshal can be used to create deep copies when needed.
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arr3 = Marshal.load Marshal.dump arr

u2.name = 'new new'

arr == arr3 #false

#17. Use the Array Method to Convert nil and Scalar Objects into Arrays

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Array(nil)  # []
Array([nil, :a]) # [nil, :a]
Array({a:12,b:323} #[:a, :b]

# Array() - First tries to call Array#to_ary on arg, then Array#to_a.

#18. Consider Set for Efficient Element Inclusion Checking

  • require 'set' before you use it.

#19. Know How to Fold Collections with reduce

  • Always use a starting value for the accumulator.
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[1,2,3].reduce(0,:+)  #6
  • The block given to reduce should always return an accumulator. It’s fine to mutate the current accumulator, just remember to return it from the block”.
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[1,2,3].reduce({}) do |map, e|
    map[e.to_s] = e
    map
end

#20. Consider Using a Default Hash Value

#21. Prefer Delegation to Inheriting from Collection Classes