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@@ -19,3 +19,77 @@
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`args[:library] << self`が、`Book`の`initialize`にあるので、`Book`オブジェクトを作る度にその引数で指定したライブラリーに追加することになります。
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#追記
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演算子メソッドの定義がわかりにくいと言うことであれば、下記でも同じです。
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```Ruby
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class Library
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def initialize
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@books = []
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end
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def add(book)
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@books << book
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end
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def to_s
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puts "Library contents:"
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@books.join("\n")
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end
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end
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class Book
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attr_accessor :author, :title
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def initialize(args)
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@author = args[:author]
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@title = args[:title]
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args[:library].add(self)
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end
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def to_s
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"Title: " + @title + ", Author: " + @author
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end
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end
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my_library = Library.new
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Book.new(:author => "Herman Melville", :title => "Moby-Dick", :library => my_library)
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Book.new(:author => "Hans Christian Andersen", :title => "The Ugly Duckling", :library => my_library)
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puts my_library
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```
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