Use of ly:set-default-scale

[Felipe Gonçalves Assis]

Hi,

In the attached snippet, the call to ly:set-default-scale has no
effect on the midi result, both in the stable and development
versions.

I believe that this is due to Pitches being constructed before
the new default_global_scale is set (see files lily/pitch.cc and
lily/scale.cc), so that they keep a pointer to the old Scale,
created in scm/lily.scm:387.

This looks bad, because as ly:set-default-scale is called, the
old object gets unprotected.

In fact, by applying the change described in the attached file
diff.txt, I obtained the results I expected (set-scale-test-mine.midi),
which only confirms my suspicions. (The last c is 6 tones higher,
because an octave is hard-coded as 6 tones, but that is another
issue).

This leads me to the following questions:

1. Is the current behaviour the desired one?
2. Is it a bug?
3. Do we really have a problem with garbage collection?
    (I observe no consequences)

By the way, there is actually an alternative solution, which would be
to make Pitch objects use default_global_scale directly, instead of
storing its value as an internal field during initialisation. This leads
me to the related question:

4. What is the purpose of the non-static scale_ field in the Pitch class?

I look forward to and would very much appreciate any thoughts on
these from anybody acquainted with this code.

Kind regards,
Felipe

diff.txt
Description: Text document

set-scale-test.ly
Description: Text Data

set-scale-test-mine.midi
Description: MIDI audio