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string = String.new  # or name = ""
string.concat('Rika')    # => Rika
string.upcase    # => RIKA
string.downcase  # => rika
string.reverse   # => akiR
string.split('') # => ["R", "i", "k", "a"]

array = Array.new  # or array = []
array.push(1)  # => [1]
array.push(2)  # => [1, 2]
array.push(3)   # => [1, 2, 3]
array.reverse  # => [3, 2, 1]
array.first    # => 1
array.last     # => 3
array[0]       # => 1
array[1]       # => 2
array[2]       # => 3

hash = Hash.new # or hash = {}
hash['first'] = "Rika" # => { 'first' => 'Rika' }
hash['last'] = "Fama"  # => { 'first' => 'Rika', 'last' => 'Fama' }

hash['first']  # => Rika
hash['last']   # => Fama

hash['first_name'].reverse  # => akiR

array.push(name)    # => [1, 2, 3, { 'first' => 'Rika', 'last' => 'Fama' } ]
array.last          # => { 'first' => 'Rika', 'last' => 'Fama' }