[ruby-core:73537] [Ruby trunk - Feature #12024] Add String.buffer, for creating strings with large capacities

Issue #12024 has been updated by Yui NARUSE.


More effective example.

```
%  cat test.rb; ./ruby test.rb
# frozen_string_literal: true
require 'benchmark'
M = 100
N = 25
Benchmark.bm 5 do |r|
  r.report "buffer" do
    j = 0
    while j < M
      i = 0
      buf = String.buffer(2**N)
      buf << "a"
      while i < N
        buf << buf
        i += 1
      end
      j += 1
    end
  end
  r.report "normal" do
    j = 0
    while j < M
    i = 0
    buf = String.new
    buf << "a"
    while i < N
      buf << buf
      i += 1
    end
      j += 1
    end
  end
end
            user     system      total        real
buffer  0.976562   1.070312   2.046875 (  2.048577)
normal  2.085938   2.867188   4.953125 (  4.954006)
```

----------------------------------------
Feature #12024: Add String.buffer, for creating strings with large capacities
https://bugs.ruby-lang.org/issues/12024#change-56750

* Author: Jeremy Evans
* Status: Open
* Priority: Normal
* Assignee: 
----------------------------------------
If you know you are going to need to create a large string,
it's better to create it with a large capacity.  Otherwise,
ruby will need to continuously resize the string as it grows.
For example, if you will be producing a string that is
100000 bytes, String.buffer(100000) will avoid 10 separate
resizes compared to using String.new.

Performance-wise, String.new is 1.33x slower than
String.buffer(100000) if appending in 1000 byte chunks,
and 1.64x slower than String.buffer(1000) if appending
in 100 byte chunks.

To make sure this works correctly with String subclasses,
a static rb_str_buf_new_with_class function is added, which
both String.buffer and rb_str_buf_new now call.


---Files--------------------------------
0001-Add-String.buffer-for-creating-strings-with-large-ca.patch (3.53 KB)


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