Strange_ruby

hash = {name: 'Olle', age: 12}
struct = Struct.new(:name, :age).new('Olle', 12)

p hash.name rescue 'NoMethodError'
p hash[:name] # => "Olle"

p struct.name # => "Olle"
p struct[:name] # => "Olle"

p hash[:color] # => nil
p struct.color rescue 'NoMethodError'

p hash.key?(:name) # => true
p hash.member?(:name) # => true
# So, in a Hash member? is alias for key?

# Struct do not have the method .key?
p struct.key?(:name) rescue 'NoMethodError'

# It has the method .member?
p struct.member?(:name) # => false

# And the struct method .member? check the values.. not the keys. 
p struct.values # => ["Olle", 12]
p struct.member?('Olle') # => true

# If you want to see the members.. just use .members
# (but do not check if a member is present with .member?)
p struct.members # => [:name, :age]

# Is this how we are supposed to check if a member (key) is present?
p struct.members.include?(:name) # => true

p '-'*80

# A Struct must be checked like this
p begin
  struct.surpuppa
rescue NoMethodError
  # will return nil
end # => nil

# or like this

p struct.surpuppa if struct.members.include?(:surpuppa) # no output

p local_variables # => [:hash, :struct, :kossa]
if 13 == 100
  kossa = 'mu'
end

# local variable kossa is created and set to nil just being mentioned
# inside a conditional (false) block.
p my_unassigned_variable rescue 'NameError'
p kossa # => nil

str = Struct.new(:name, :age, :xtra).new('Olle', 13, nil)

class Struct
  alias :value? :member?
  def member?(key) = self.members.include?(key)
  
  def on_member(key, &bl)
    (yield(self[key]) if member?(key)) if bl
  end
end

p str.member? :xtra #   => true
p str.member? :ixtra #  => false
p str.value? 'arne' #   => true
p str.value? 37 #       => false


str.on_member(:name)    { p it }
str.on_member(:fis)     { p 'will not print' }
str.on_member(:xtra)    { p 'that is a nil value' }