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[py2rb] 部分適用

Last updated at Posted at 2022-02-09

はじめに

移植やってます。
( from python 3.7 to ruby 2.7 )

partial (Python)

from functools import partial

def partial_func(name, value):
    print(name, value)

func1 = partial(partial_func, 'aa')

func1('bb')

# aa bb

ふむふむ。

どうすRuby

lambda.rb
func2 = lambda do |name|
  partial_func = lambda do |value|
    puts "#{name} #{value}"
  end
end

func1 = func2.call('aa')
func1.call('bb')

func2.call('aa').call('bb')

引数を2回に分けて渡すと考えるなら、lambdaでも良さそう。
ありそうなパターン

消費税設定 = lambda do |消費税|
  partial_func = lambda do |税抜き価格|
    puts (税抜き価格 * (1 + 消費税)).floor
  end
end

税込み価格 = 消費税設定.call(0.1)
税込み価格.call(100)
税込み価格.call(109)
税込み価格.call(110)

# output
110
119
121

curry
消費税設定 = lambda do |消費税, 税抜き価格|
  puts (税抜き価格 * (1 + 消費税)).floor
end.curry

税込み価格 = 消費税設定.call(0.1)
税込み価格.call(100)
税込み価格.call(109)
税込み価格.call(110)

curryすると、lambdaを二重にしなくても上手くやってくれる。

class.rb
class A
  def initialize(tax)
    @tax = tax
  end

  def taxin(value)
    puts (value * (1 + @tax)).floor
  end
end

a = A.new(0.1)
a.taxin(100)
a.taxin(109)
a.taxin(110)

まとめると、既存のメソッドを再利用する分には便利ですが、新規で作るならクラスで十分かも。

メモ

  • Python の partial を学習した
  • 百里を行く者は九十里を半ばとす
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