Need help understanding some Ruby code from

I was looking through some code in a string escape library the other day and I came across some code that looks like this:

class StringWrapper 
  class << self
    alias new_no_dup new
    def new(str)
开发者_StackOverflow社区      new_no_dup(str.dup)
    end
  end

  def initialize(str)
    @str = str
  end

  ...

end

Can anyone explain exactly what is going on here? I understand up to the class << self part, but I don't quite understand aliasing the method new to new_no_dup, only to call it in the new method below? Also, why do you think the author want to do this in this manner?

By aliasing new_no_dup to new, the original new functionality can be called by calling new_no_dup.

The StringWrapper.new method calls duplicate (.dup) on the provided string and then provides that copy to the original StringWrapper.new method.

As for why, I would assume the author is trying to prevent the original string from being changed. StringWrapper will always have it's own string in memory.

Whether you use .dup on strings influences whether in-place modifications (methods ending with !) affect the original string.

As a silly little demonstration...

irb(main):009:0> def shout(s)
irb(main):010:1>  local = s.dup
irb(main):011:1>  local.upcase!
irb(main):012:1>  puts local
irb(main):013:1> end
=> nil
irb(main):014:0> greeting = "hi"
=> "hi"
irb(main):015:0> shout(greeting)
HI
=> nil
irb(main):016:0> greeting
=> "hi"

If you run the same snippet, changing local = s.dup to local = s, then the final value of greeting will be "HI" because shout will have modified greeting. .dup returns a copy of the original string, preventing modifications to the original.