ruby-on-rails - Ruby - 哈希数组 - 未定义的方法 'each' 错误

Question

我想遍历哈希数组并将值打印到终端。

当前收到错误:

main.rb:14:in `print': undefined method `each' for nil:NilClass (NoMethodError)
from main.rb:22:in `<main>'

我想要遍历，而不是像puts @transactions这样简单的东西>

我收到此错误的任何想法？谢谢

class TestRun
   @transactions = [
      {:repayment_number => 1, :repayment_amount => 224.34},
      {:repayment_number => 2, :repayment_amount => 241.50},
      {:repayment_number => 3, :repayment_amount => 135.04},
      {:repayment_number => 4, :repayment_amount => 91.00}
   ]

   def print()
      @transactions.each do |t|
         puts "#{t[:repayment_number]} - #{t[:repayment_amount]}"
      end
   end

end

@test = TestRun.new
@test.print()

Answer 1

您已经定义了两次 @transactions，最初是当 self 等于 TestRun 时，使其成为一个类实例变量 ，然后在 print 方法中，当 self 是实例 TestRun.new 时，使它成为一个实例变量 .这两个变量与 @night 和 @day 一样不同。

以下是使您的代码正常工作的三种方法(前两种仅用于教育目的)。

使print成为类方法

class TestRun
  puts "self at class level = #{self}"
  @transactions = [
    {:repayment_number => 1, :repayment_amount => 224.34},
    {:repayment_number => 2, :repayment_amount => 241.50}
  ]
  def self.print
    puts "self within self.print = #{self}"
    @transactions.each do |t|
      puts "#{t[:repayment_number]} - #{t[:repayment_amount]}"
    end
  end
end
  #=> self at class level = TestRun
TestRun.print
  #=> self within self.print = TestRun
  #   1 - 224.34
  #   2 - 241.5

从方法 print 中访问类实例变量

class TestRun
  @transactions = [
    {:repayment_number => 1, :repayment_amount => 224.34},
    {:repayment_number => 2, :repayment_amount => 241.50}
  ]
  def print
    puts "self within print = #{self}"
    self.class.instance_variable_get(:@transactions).each do |t|
      puts "#{t[:repayment_number]} - #{t[:repayment_amount]}"
    end
  end
end

TestRun.new.print
  #=> self within print = #<TestRun:0x007fcccb13f390>
  #   1 - 224.34
  #   2 - 241.5

在初始化方法中定义@transactions，使其成为一个实例变量

这是@31piy 所做的，很可能是 OP 的意图。

class TestRun
  def initialize
    puts "self within initialize = #{self}"    
    @transactions = [
      {:repayment_number => 1, :repayment_amount => 224.34},
      {:repayment_number => 2, :repayment_amount => 241.50}
    ]
  end
  def print
    puts "self within print = #{self}"
    @transactions.each do |t|
      puts "#{t[:repayment_number]} - #{t[:repayment_amount]}"
    end
  end
end

TestRun.new.print
  #=> self within initialize = #<TestRun:0x007fcccb2ae988>
  #   self within print = #<TestRun:0x007fcccb2ae988>
  #   1 - 224.34
  #   2 - 241.5