Pattern Matching

Array Patterns

Array patterns destructure positions into named variables.

array pattern An array pattern can match shape and assign elements to local variables.

Array Patterns

amount
array_patterns.rb
Replay: real traced execution (multi-file project)
amount = 3
command = ["add", amount]

case command
in ["add", value]
  result = value + 10
in ["remove", value]
  result = 10 - value
else
  result = 0
end

puts "command=#{command.join(",")}"
puts "result=#{result}"

amount = 1
command = ["add", amount]

case command
in ["add", value]
  result = value + 10
in ["remove", value]
  result = 10 - value
else
  result = 0
end

puts "command=#{command.join(",")}"
puts "result=#{result}"

amount = 6
command = ["add", amount]

case command
in ["add", value]
  result = value + 10
in ["remove", value]
  result = 10 - value
else
  result = 0
end

puts "command=#{command.join(",")}"
puts "result=#{result}"

  1. amount ← 3, command ← ["add", 3]

    1amount→ 3 = 3  #@amount=1, 62command→ ["add", 3] = ["add", amount3]34case command5in ["add", value]6  result = value + 107in ["remove", value]8  result = 10 - value9else10  result = 011end1213puts "command=#{command.join(",")add,3}"14puts "result=#{result13}"
    outputcommand=add,3
result=13

  1. amount ← 1, command ← ["add", 1]

    1amount→ 1 = 12command→ ["add", 1] = ["add", amount1]34case command5in ["add", value]6  result = value + 107in ["remove", value]8  result = 10 - value9else10  result = 011end1213puts "command=#{command.join(",")add,1}"14puts "result=#{result11}"
    outputcommand=add,1
result=11

  1. amount ← 6, command ← ["add", 6]

    1amount→ 6 = 62command→ ["add", 6] = ["add", amount6]34case command5in ["add", value]6  result = value + 107in ["remove", value]8  result = 10 - value9else10  result = 011end1213puts "command=#{command.join(",")add,6}"14puts "result=#{result16}"
    outputcommand=add,6
result=16