Object subclass: Book [
    | title borrowed |
 
    Book class >> title: aString [
        ^self new initTitle: aString
    ]
 
    initTitle: aString [
        title := aString.
        borrowed := false.
        ^self
    ]
 
    title [
        ^title
    ]
 
    isBorrowed [
        ^borrowed
    ]
 
    borrow [
        borrowed := true.
    ]
 
    returnBook [
        borrowed := false.
    ]
]
 
Object subclass: User [
    | name |
 
    User class >> name: aString [
        ^self new initName: aString
    ]
 
    initName: aString [
        name := aString.
        ^self
    ]
 
    name [
        ^name
    ]
]
 
Object subclass: Library [
    | books |
 
    Library class >> newLibrary [
        ^self new init
    ]
 
    init [
        books := OrderedCollection new.
        ^self
    ]
 
    addBook: aBook [
        books add: aBook.
    ]
 
    borrowBook: aBook by: aUser [
        (aBook isBorrowed)
            ifTrue: [
                Transcript show: '貸出中'; cr.
            ]
            ifFalse: [
                aBook borrow.
                Transcript show: aUser name;
                    show: ' が ';
                    show: aBook title;
                    show: ' を借りました'; cr.
            ].
    ]
 
    returnBook: aBook [
        aBook returnBook.
        Transcript show: aBook title;
            show: ' を返却しました'; cr.
    ]
]
 
| library book1 user1 |
 
library := Library newLibrary.
 
book1 := Book title: 'オブジェクト指向入門'.
 
user1 := User name: '佐藤'.
 
library addBook: book1.
 
library borrowBook: book1 by: user1.
 
library returnBook: book1.

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