Beware ||= operator when dealing with booleans

You can use ||= operator for caching variables:

def pi
  @pi ||= Pi.compute_precisely
end

Just watch out when dealing with booleans, especially if the result of function is time-dependent or nondeterministic:

def schrodingers_cat_dead?
  @dead ||= rand < 0.5
end

schrodingers_cat_dead? # => false
schrodingers_cat_dead? # => false
schrodingers_cat_dead? # => true

In this case @dead caching variable is evaluated until it become true. That's because !!nil == false. Instead you should write:

def schrodingers_cat_dead?
  @dead = rand < 0.5 if @dead.nil?
  @dead
end

schrodingers_cat_dead? # => false
schrodingers_cat_dead? # => false
schrodingers_cat_dead? # => false