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Ruby - Proc vs Lambda

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  • lambda 會檢查參數的個數
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def args(code)
  code.call(1, 2, 3, 4)
end

# 也可以寫 proc { |x, y, z| x + y + z }
proc = Proc.new { |x, y, z| x + y + z }
lambda = lambda { |x, y, z| x + y + z }

args(proc)
# => 6
args(lambda)
#ArgumentError: wrong number of arguments (4 for 3)
  • lambda 的 return 會繼續執行，proc 則會直接終止
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def proc_return
  Proc.new { return "Proc.new" }.call
  return "proc_return method finished"
end

def lambda_return
  # 也可以寫成 lambda { return "lambda" }
  -> { return "lambda" }.call
  return "lambda_return method finished"
end

proc_return
# => "Proc.new"
lambda_return
# => "lambda_return method finished"

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def generic_return(code)
  one, two    = 1, 2
  three, four = code.call(one, two)
  "#{three} and #{four}"
end

generic_return(-> (x, y){ return x + 1, y + 2 })
# 也可以寫成 lambda { |x, y| return x + 1, y + 2 }
#  => "2 and 4"
generic_return(Proc.new { |x, y| return x + 1, y + 2 })
# LocalJumpError: unexpected return
generic_return(Proc.new { |x, y| x + 1; y + 2 })
#  => "4 and "
generic_return(Proc.new { |x, y| [x + 1, y + 2] })
#  => "2 and 4"

參考文件

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