From: Robert Klemme <shortcutter@...>
Date: 2008-12-19T17:26:10+09:00
Subject: [ruby-core:20692] Re: [Feature #905] Add String.new(fixnum) to preallocate large buffer

2008/12/19 Martin Duerst <duerst@it.aoyama.ac.jp>:
> At 09:08 08/12/19, Brian Ford wrote:
>
>>Something like "ab" * 5 then becomes String.pattern("ab".size * 5, "ab").
>
> I'm at a total loss to see why
>   String.pattern("ab".size * 5, "ab")
> should be in any way better than
>   "ab" * 5
> but maybe that's just me. Can somebody explain?

It's probably not.  But if you want "ab" repeated 5 times, then "ab" *
5 is probably the ideal solution.

Fixing the length in bytes is a new and different feature, i.e. your
pattern is cut off.  With String.pattern("bo",3) you would get "bob"
or maybe "bo" but in a buffer of length 3 bytes.

We could also name it "resize" with this semantics:

String.resize(100, "foo") -> "foo" and buffer has 100 bytes
String.resize(100) -> "" and buffer has 100 bytes

Or maybe just "size".  IMHO the idea was that you do not need to have
a String beforehand so all solution which are instance methods receive
a String as argument are probably suboptimal because they will
typically be invoked like show above, i.e. with a String constructor
which needs one object allocation (including GC bookkeeping overhead)
and a bit of memory.

A typical use case would be this:

File.open "foo" do |io|
  buffer = String.size(1024)
  while io.read(1024, buffer)
    # or even io.read(buffer.capacity, buffer)
    $defout.write(buffer)
  end
end

Kind regards

robert

-- 
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