[ruby-core:46442] [ruby-trunk - Feature #6733][Open] New inspect framework

Issue #6733 has been reported by akr (Akira Tanaka).

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Feature #6733: New inspect framework
https://bugs.ruby-lang.org/issues/6733

Author: akr (Akira Tanaka)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 3.0


After we discussed http://bugs.ruby-lang.org/issues/6291 at a developer meeting,
we re-realized new inspect framework may be useful.

Problem:
* inspect method may generate too long string but sometimes whole string is not required.
  For example, first 70 characters are enough for error messages (backtrace).
* inspect can't know a encoding to be expected.
* inspect generates may short strings and discard them immediately.

If we have a new method, inspect_to(buffer), and
it (or overridden method in subclass) adds the inspected result to buffer,
we can solve above problems.
buffer has a method, <<.
It may be a string, IO or other object.

For too long string, buffer itself can throw (or raise) when buffered output is reached to a specified limit.

For encoding, buffer can record an encoding.
(p method creates a buffer object using $stdout's encoding.)

For small strings, in C level, we can create a rb_buffer_add(VALUE buffer, const char *p, long len) and
it don't need to allocate a String object.

This is big change but we can preserve compatibility by following default inspect_to method:

class Object
  def inspect_to(buffer)
    buffer << self.inspect
  end
end

If legacy class which has inspect but not inspect_to,
Object#inspect_to calls inspect and use the result.



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