Some examples of blocks, including our own implementation of select

blocks.rb

def do_some_maths
  puts yield(10)
  puts yield(20)
end

do_some_maths do |num|
  num * 20
end

do_some_maths do |number|
  number - 5 * 35
end

def select(arr)
  selected_values = []

  arr.each do |value|
    if yield(value)
      selected_values << value
    end
  end

  selected_values
end

arr = [1,2,3,4]

select(arr) { |array_value| array_value.odd? }
select(arr) { |array_value| array_value.even? }
puts select(arr) { |array_value| array_value > 2 }.inspect