Ruby类如何工作

Question

这是odin项目的一个练习，他们给你一个带有测试规范的文件，你必须编写程序来传递它们。

程序的工作，但我刚开始Ruby类，我不明白为什么，如果我做了修改，我会告诉不起作用：

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 

    it 'should capitalize every word' do 
     @book.title = "stuart little" 
     @book.title.should == "Stuart Little" 
    end 

    describe 'should capitalize every word except...' do 
     describe 'articles' do 
     specify 'the' do 
      @book.title = "alexander the great" 
      @book.title.should == "Alexander the Great" 
     end 

     specify 'an' do 
      @book.title = "to eat an apple a day" 
      @book.title.should == "To Eat an Apple a Day" 
     end 
     end 

     specify 'conjunctions' do 
     @book.title = "war and peace" 
     @book.title.should == "War and Peace" 
     end 

     specify 'the first word' do 
     @book.title = "the man in the iron mask" 
     @book.title.should == "The Man in the Iron Mask" 
     end 
    end 
    end 
end 

代码

class Book 
    def title 
    @title 
    end 

    def title=(title) 
    @title = titlieze(title) 
    end 

    private 
    def titlieze(title) 
    stop_words = %w(and in the of a an) 
    title.capitalize.split.map{|w| stop_words.include?(w) ? w : w.capitalize}.join(' ') 
    end 

end 

为什么，如果我写我这样的代码

class Book 

    def title=(title) 
    @title = titlieze(title) 
    @title 
    end 

    private 
    def titlieze(title) 
    stop_words = %w(and in the of a an) 
    title.capitalize.split.map{|w| stop_words.include?(w) ? w : w.capitalize}.join(' ') 
    end 

end 

然后我得到这个错误：

Failure/Error: expect(@book.title).to eq("Inferno") 

    NoMethodError: 
     undefined method `title' for #<Book:0x000000017bd0a8 @title="Inferno"> 
     Did you mean? title= 

但这种方法“标题”没有定义？为什么它说不是？

Answer 1

因为def title=(title)定义了设置器方法名为title=为@title变量赋值。重要的是要注意=是方法名称的一部分。

虽然说明书抱怨缺少获取方方法名为title（没有=）。

您的第二个版本缺少titlegetter方法为@title变量。你可能只是使用attr_reader宏添加这样一个getter方法：

class Book 
    attr_reader :title 

    # ... 
end 

attr_reader :title仅仅是在你的第一个版本生成的方法等的快捷方式：当在规范中写着“

def title 
    @title 
end