Ruby's pattern matching

pattern_matching.rb

# pattern matching on blocks

def print_break(msg)
  puts '-' * 50, msg
end

print_break 'normal params'
block = -> (one, two) { p one, two }
block.call(1, 2)
# 1
# 2

print_break 'splat params'
block = -> (*args) { p args }
block.call(3, 4)
# [3, 4]

print_break 'normal params mixed with splat'
block = -> (head, *tail) { p head, tail }
block.call(5, 6, 7, 8)
# 5
# [6, 7, 8]

print_break 'normal params mixed with splat ignoring a value'
block = -> (_, *tail) { p tail }
block.call(5, 6, 7, 8)
# [6, 7, 8]

print_break 'splat mixed in the middle'
block = -> (first, *middle, last) { p first, middle, last }
block.call(5, 6, 7, 8)
# 5
# [6, 7]
# 8

print_break 'splat mixed in the middle'
block.call(5, 8)
# 5
# []
# 8

print_break 'assignments'
_, *tail = [1, 2, 3, 4]
p tail

head, _  = [1, 2, 3,4]
p head

*init, _  = [1, 2, 3,4]
p init

print_break 'tuples'
[
  ["First Name", "Hercules"], 
  ["Last Name",  "Merscher"] 
].each do |(key, value)|
  puts "#{key}: #{value}"
end
# First Name: Hercules
# Last Name: Merscher

{ first_name: "Hercules", last_name: "Merscher" }.each do |(key, value)|
  puts "#{key}: #{value}"
end
# first_name: Hercules
# last_name: Merscher