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Question

下面是我知道的一些代码：

require 'csv'

class Motorcycle
  attr_reader :name, :weight
  @@count = 0

  def self.find (name)
    found = nil
    ObjectSpace.each_object(Motorcycle) { |o|
      found = o if o.name == name
    }
    return found
  end

  def self.create
    File.new('motorcycles.csv').readlines[1..-1].map{ |line|
        Motorcycle.new( *line.split( ',' )  )
    }
  end

  def initialize (name, weight)
    @name = name
    @weight = weight
    self.class.count += 1
  end

  def self.count
    return @@count
  end

  def self.count=( count ) 
    @@count = count 
  end

  def available_colors

    colors=[]
    colorsFile = File.read('colors.csv').split("\n").map { |line| line.split(',') }
    for i in (0..colorsFile.flatten.length) do
        if (colorsFile.flatten[i].to_s == self.name.to_s)
            colors.push(colorsFile.flatten[i+1])
        end
    end

    return colors
  end

  def contains (name,color)
    if(self.name.to_s == name)
    else
        return color
    end
  end

  def has_abs?
    File.open( 'abs.txt' ) do |io|
    io.each {|line| line.chomp! ; return true if line.include? self.name.to_s}
    end

    return false
  end

end

Motorcycle.create

代码必须通过rspec上的以下测试：

describe Motorcycle do
  describe "loading the motorcycle list" do
    it "should load 2 motorcycles from the CSV" do
      Motorcycle.count.should == 2
    end
  end

  describe "finding a motorcycle by name" do
    it "should return an instance of the Motorcycle class" do
      Motorcycle.find("1200 RT").should be_a Motorcycle
    end    
  end

  describe "#weight" do
    it "should have a weight of 800 pounds for the 1200 RT" do
      Motorcycle.find("1200 RT").weight.should == '800 pounds'
    end

    it "should have a weight of 500 pounds for the 600 GS" do
      Motorcycle.find("600 GS").weight.should == '500 pounds'
    end
  end

  describe "#available colors" do
    it "should find 'red' and 'black' as available colors for the BMW 1200 RT" do
      Motorcycle.find("1200 RT").available_colors.should == [ 'red', 'black' ]
    end

    it "should find 'green' and 'blue' as available colors for the BMW 600 GS" do
      Motorcycle.find("600 GS").available_colors.should == [ 'green', 'blue' ]
        end    
  end

  describe "#has_abs?" do
    it "should be true for a motorcycle that appears in abs_motorcycles.txt" do
      Motorcycle.find("1200 RT").has_abs?.should be_true
    end

    it "should be false for a motorcycle that does not appear in abs_motorcycles.txt" do
      Motorcycle.find("600 GS").has_abs?.should be_false
    end
  end
end

问题是，在第一次测试(其中它计算motrocicle实例的数量)之后，每个实例都是零，也就是说，除了第一个之外，所有的测试都失败了。以下是输出日志：

Failures:

  1) Motorcycle finding a motorcycle by name should return an instance of the Motorcycle class
     Failure/Error: Unable to find matching line from backtrace
       expected nil to be a kind of Motorcycle
     # ./motoapp.rb:76

  2) Motorcycle#weight should have a weight of 800 pounds for the 1200 RT
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `weight' for nil:NilClass
     # ./motoapp.rb:82

  3) Motorcycle#weight should have a weight of 500 pounds for the 600 GS
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `weight' for nil:NilClass
     # ./motoapp.rb:86

  4) Motorcycle#available colors should find 'red' and 'black' as available colors for the BMW 1200 RT
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `available_colors' for nil:NilClass
     # ./motoapp.rb:92

  5) Motorcycle#available colors should find 'green' and 'blue' as available colors for the BMW 600 GS
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `available_colors' for nil:NilClass
     # ./motoapp.rb:96

  6) Motorcycle#has_abs? should be true for a motorcycle that appears in abs_motorcycles.txt
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `has_abs?' for nil:NilClass
     # ./motoapp.rb:102

  7) Motorcycle#has_abs? should be false for a motorcycle that does not appear in abs_motorcycles.txt
     Failure/Error: Unable to find matching line from backtrace
     NoMethodError:
       undefined method `has_abs?' for nil:NilClass
     # ./motoapp.rb:106

Finished in 0.01223 seconds
8     examples, 7 failures

我一直倾向于认为这是某种bug或什么，因为我的手动测试结果是这样的：

puts Motorcycle.count
puts Motorcycle.find("1200 RT")
puts Motorcycle.find("1200 RT").weight
puts Motorcycle.find("600 GS").weight
puts Motorcycle.find("1200 RT").available_colors
puts Motorcycle.find("600 GS").available_colors
puts Motorcycle.find("1200 RT").has_abs?
puts Motorcycle.find("600 GS").has_abs?

这给了我这个输出：

2
#<Motorcycle:0x7fd8bffcfd88>
800 pounds
500 pounds
red
black
green
blue
true
false

所以我真的走进了死胡同，有谁知道可能会发生什么吗？

Answer 1

在我看来，在执行create调用时，您并没有将Motorcycle对象存储在任何地方，所以如果调用了GC，这些实例就会消失。加载更多的ruby代码(rspec)可能会导致GC的调用更快。

为什么不直接将实例存储在类级Set中呢？(例如，将count调用替换为instances << self)或Hash(以实例名称作为键存储实例)

另外，在我看来，当你应该有一个从CSV读取的before块时，你是在依赖于rspec的执行顺序。

示例代码：

Class Motorcycle
 # use a constant, this will always point to the same object even though
 # the content of the object changes. 
 # Using @@instances would also be ok
 Instances = Set.new # or you can use Instances = Hash.new
 def initialize (name, weight)
   @name = name
   @weight = weight
   # 
   Instances << self # or store the name/instance mapping Instances[name] = self
 end