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class Array
  def my_map
    ary = []
    
    self.each do |elem|
      ary << yield(elem)
    end
    
    ary
  end

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def yield_with_return_value
  hello_world = yield

  puts hello_world
end

yield_with_return_value { "Hello World!" } # => Hello World!

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def yield_with_arguments
  hello = 'Hello'
  world = 'World!'

  yield(hello, world)
end

yield_with_arguments { |hello, world| puts "#{hello} #{world}" } # => Hello World!

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def optional_block
  yield if block_given?
end

optional_block # => nil
optional_block { puts 'optional block' } # => optional block

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def yield_without_block
  yield
end

yield_without_block # => LocalJumpError (no block given (yield))

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def one_yield
  yield
end

def multiple_yields
  yield
  yield
end

one_yield { puts "one yield" }

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computer.cores = 2

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computer[:screens] = 2

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require 'ostruct'

computer = OpenStruct.new(ram: '4GB')

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computer.instance_variables # => [:@table, :@modifiable]