Pattern Matching

Hash Patterns

Hash patterns match required keys and bind their values.

hash pattern A hash pattern can require keys and assign their values to variables.

Hash Patterns

kind
hash_patterns.rb
Replay: real traced execution (multi-file project)
kind = "click"
event = { kind: kind, x: 4, y: 7 }

case event
in { kind: "click", x: x, y: y }
  summary = "click #{x},#{y}"
in { kind: "view" }
  summary = "view event"
else
  summary = "ignored"
end

puts "kind=#{kind}"
puts "summary=#{summary}"

kind = "view"
event = { kind: kind, x: 4, y: 7 }

case event
in { kind: "click", x: x, y: y }
  summary = "click #{x},#{y}"
in { kind: "view" }
  summary = "view event"
else
  summary = "ignored"
end

puts "kind=#{kind}"
puts "summary=#{summary}"

kind = "skip"
event = { kind: kind, x: 4, y: 7 }

case event
in { kind: "click", x: x, y: y }
  summary = "click #{x},#{y}"
in { kind: "view" }
  summary = "view event"
else
  summary = "ignored"
end

puts "kind=#{kind}"
puts "summary=#{summary}"

  1. kind ← click, event ← {:kind=>"click", :x=>4, :y=>7}

    1kind→ click = "click"  #@kind="view", "skip"2event→ {:kind=>"click", :x=>4, :y=>7} = { kind: kindclick, x: 4, y: 7 }34case event5in { kind: "click", x: x, y: y }6  summary = "click #{x},#{y}"7in { kind: "view" }8  summary = "view event"9else10  summary = "ignored"11end1213puts "kind=#{kindclick}"14puts "summary=#{summaryclick 4,7}"
    outputkind=click
summary=click 4,7

  1. kind ← view, event ← {:kind=>"view", :x=>4, :y=>7}

    1kind→ view = "view"2event→ {:kind=>"view", :x=>4, :y=>7} = { kind: kindview, x: 4, y: 7 }34case event5in { kind: "click", x: x, y: y }6  summary = "click #{x},#{y}"7in { kind: "view" }8  summary = "view event"9else10  summary = "ignored"11end1213puts "kind=#{kindview}"14puts "summary=#{summaryview event}"
    outputkind=view
summary=view event

  1. kind ← skip, event ← {:kind=>"skip", :x=>4, :y=>7}

    1kind→ skip = "skip"2event→ {:kind=>"skip", :x=>4, :y=>7} = { kind: kindskip, x: 4, y: 7 }

  2. case event in { kind:

    4case event{:kind=>"skip", :x=>4, :y=>7}5in { kind: "click", x: x, y: y }6  summary = "click #{x},#{y}"

  3. summary ← ignored

    8  summary = "view event"9else10  summary→ ignored = "ignored"11end

  4. puts "kind=#{kind}"

    13puts "kind=#{kindskip}"14puts "summary=#{summaryignored}"
    outputkind=skip
summary=ignored