ruby - 不懂 Ruby ljust/rjust/center 方法

Question

我正在学习嵌套，我的任务是让每一行都以缩进开头。这是我的代码，但它不起作用

$nestingDepth = 0

def logger description, &block
    puts "Beginning #{description}".rjust($nestingDepth)
    puts $nestingDepth
    $nestingDepth = $nestingDepth + 10
    result = block.call
    $nestingDepth = $nestingDepth - 10
    puts $nestingDepth
    puts "End of #{description} block that returned #{result}".rjust($nestingDepth)
end

logger "first block" do 
    logger "second block" do
        logger "third block" do 
            puts "third block part"
        end
        puts "second block part"
    end
    puts "first block part"
end

Answer 1

您的代码有几个问题:

• 您正在使用全局变量，这通常不是一个好主意，请将其作为参数传递下去。为此，您可以使用定义记录器和记录方法的 DSL 类。
• 您在 block 内调用 puts，但您从未更改它的定义，我不明白您期望它如何打印缩进字符串，它只会正常打印字符串没有缩进。为此，您需要定义一个特殊的方法来打印缩进，例如日志
• 您正在调用 rjust 并希望它缩进字符串。这个方法有不同的目的——用指定的长度向右对齐一个字符串(即左填充)。如果字符串长于指定长度，则返回原始字符串。要实际缩进一个字符串，您应该执行 puts ' ' * nestingDepth + string。一开始看起来很神奇，但是 * 运算符只是重复字符串，例如'abc' * 3 #=> 'abcabcabc'

总而言之，我会这样做:

class DSL
  def initialize
    @depth = 0
  end

  def logger(description, &block)
    log "Beginning #{description}"
    @depth += 1
    result = instance_eval(&block)
    @depth -= 1
    log "End of #{description} that returned #{result}"
  end

  def log(string)
    puts indent + string
  end

  private

  def indent
    ' ' * (10 * @depth)
  end
end

def logger(*args, &block)
  DSL.new.logger(*args, &block)
end

例子:

logger "first block" do 
  logger "second block" do
    logger "third block" do 
      log "third block part"
    end
    log "second block part"
  end
  log "first block part"
end

这打印:

Beginning first block
          Beginning second block
                    Beginning third block
                              third block part
                    End of third block that returned
                    second block part
          End of second block that returned
          first block part
End of first block that returned