当字符串太长时截断字符串

Question

我有两个字符串:

short_string = "hello world"
long_string = "this is a very long long long .... string" # suppose more than 10000 chars

我想将默认行为更改print为:

puts short_string
# => "hello world"
puts long_string
# => "this is a very long long....."

的long_string仅部分打印.我试图改变String#to_s,但它没有用.有谁知道怎么做这样吗？

更新

实际上我想它运作顺利,这意味着以下情况也可以正常工作:

> puts very_long_str
> puts [very_long_str]
> puts {:a => very_long_str}

所以我认为这种行为属于String.

无论如何,谢谢大家.

Answer 1

首先,你需要truncate一个字符串的方法,如下所示:

def truncate(string, max)
  string.length > max ? "#{string[0...max]}..." : string
end

或者通过扩展String:(不建议改变核心类)

class String
  def truncate(max)
    length > max ? "#{self[0...max]}..." : self
  end
end

现在您可以truncate在打印字符串时调用:

puts "short string".truncate
#=> short string

puts "a very, very, very, very long string".truncate
#=> a very, very, very, ...

或者您可以定义自己的puts:

def puts(string)
  super(string.truncate(20))
end

puts "short string"
#=> short string

puts "a very, very, very, very long string"
#=> a very, very, very, ...

请注意,Kernel#puts采用可变数量的参数,您可能需要相应地更改puts方法.

Answer 2

这就是Ruby on Rails在String#truncate方法中的作用.

def truncate(truncate_at, options = {})
  return dup unless length > truncate_at

  options[:omission] ||= '...'
  length_with_room_for_omission = truncate_at - options[:omission].length
  stop =        if options[:separator]
      rindex(options[:separator], length_with_room_for_omission) || length_with_room_for_omission
    else
      length_with_room_for_omission
    end

  "#{self[0...stop]}#{options[:omission]}"
end

然后你可以像这样使用它

'And they found that many people were sleeping better.'.truncate(25, omission: '... (continued)')
# => "And they f... (continued)"

是的.它添加到Rails作为猴子补丁.所以它实现如下:

class String
  def truncate..
  end
end