From: Robert Klemme <shortcutter@...>
Date: 2009-12-06T21:35:04+09:00
Subject: Re: Why doesn't Ruby "compile" strings?

On 06.12.2009 11:17, Brian Candler wrote:
> Iņaki Baz Castillo wrote:
>>> When you are using the string literals, the interpreter doesn't know what
>>> you are going to do with that string literal, so it's not really safe for
>>>  it to assume that it can use a single ruby object to represent all
>>>  instances of it.
>> Why not? It's obviously a string writen in the script, with no variables 
>> into
>> it and so...
> 
> Suppose you do:
> 
>   10.times do
>     puts "hello"
>   end
> 
> The interpreter has no way of knowing that puts does not mutate the 
> argument passed to it. This is a silly example, but you might have done:
> 
>   alias :old_puts :puts
>   def puts(x)
>     old_puts x
>     x.replace "rubbish"
>   end
> 
> So it is forced to create a new string object each time round the loop.
> 
> It's a shame that Ruby doesn't have immutable strings. Symbols are the 
> closest, but they have different semantics to strings.
> 
> If the literal syntax "xxx" gave a *frozen* String, then it would be 
> safe to re-use it. But then if you wanted to append to a string, you'd 
> have to write:
> 
>   a = "".dup
>   a << "stuff"
> 
> or perhaps
> 
>   a = String.new
>   a << "stuff"

Another thing you could not do with the auto interning (as with Java 
String constants):

...each do |whatever|
   s = "intro " << whatever << " outro"
   store_away(s)
end

Ruby leaves the decision up to you where you want to optimize while 
still keeping things nice for other use cases.  The code above would 
have to look like this if "" and '' would not construct new objects:

...each do |whatever|
   s = "intro ".dup << whatever << " outro"
   store_away(s)
end

Now, that looks worse IMHO.

Kind regards

	robert


PS: Note also that all strings created via "" and '' do share the 
internal character buffer until one of them is modified (copy on write) 
so it could be more inefficient as it actually is. :-)

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/