Ruby中的類，對象和setter方法？

Question

試圖瞭解如何使用setter methods爲什麼我在這裏失敗？我不明白我做錯了什麼。有人可以解釋嗎？謝謝。

class Book 
    def title=(title) 
    @title = title.capitalize 
    end 
end 

Rspec的

describe Book do 
    before do 
    @book = Book.new 
    end 

    describe 'title' do 
    it 'should capitalize the first letter' do 
     @book.title = "inferno" 
     @book.title.should == "Inferno" 
    end 
    end 
end 

測試失敗：

Book title should capitalize the first letter Failure/Error: @book.title.should == "Inferno"

NoMethodError:

undefined method `title' for #<Book:0x00000104abd538 @title="Inferno"> 
# ./ct.rb:865:in `block (3 levels) in <top (required)>' 

Answer 1

當你這樣做：

@book.title.should == "Inferno" 

喲你實質上是在Book對象上調用title方法，這當然不存在。您只定義了設置器。

你也必須定義吸氣：

class Book 
    def title 
    @title 
    end 

    # ... 
end 

請注意，沒有定義這兩個調節器和吸氣的縮寫：

class Book 
    attr_accessor :title 
end