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Effective Ruby

Effective Ruby

#1 (Almost) Everything is true

  • Every value is true except false and nil.
  • The number zero is true in Ruby.
  • Use the nil? method to differentiate between false and nil.

#2 All objects could be nil

  • Coerce nil objects into the expected type (eg use to_i and to_s).
  • Array#compact/Hash#compact removes all nil elements.
  • Array#dig/Hash#dig returns nil if any intermediate step is nil.

#3 -

#4 Constants are mutable

  • Always freeze constants to prevent them form being mutated (eg TIMEOUT = 5.freeze).

#5 -

#6 -

#7 Different behaviours of super

  • When you override a method from inheritance hierarchy the super keyword can be used to call the overriden method.
  • Using super with no arguments and parentheses is equivalent to passing it all of the arguments that were given to the enclosing method.
  • If you want to use super without passing the overriden method any arguments, you must use empty parentheses (eg super()).

#8 -

#9 -

#10 Struct for structured data

  • When dealing with structured data which doesn't quite justify a new lass prefer using Struct to Hash.
  • Assign the return value of Struct::new to a constant and treat that constant like a class (eg Reading = Struct.new(:date, :high, :low))

#11 -

#12 Different flavors of equality

  • Never ovveride the equal? method. It's expected to strictly compare objects and return true only if they're both pointers to the same object in memory (have the same object_id).
  • The Hash class uses the eql? method to compare objects used as keys during collisions. The default implementation probably doesn't do what you want. You need to implement <=>, then alias eql? to == and write a sensible hash method.
  • Use the == operator to test if two objects represent the same value.
  • case expressions use the === operator to test each when clause. The left operand is the argument given to when and the right operand is the argument given to case.

13 Compare 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.

14 -

15 Class instance variables over class variables

  • Prefer class instance variables to class variables.
  • Classes are objects and so have their own private set of instance variables.

16 Duplicate collections before mutating them

  • Method arguments are passed as references, not values (except Fixnum objects).
  • Duplicate collections passed as arguments before mutating them, eg @collection = collection.dup.
  • The dup and clone methods only create shallow copies. For most objects, Marshal can be used to create deep copies.

References

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