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Re: Use of ly:set-default-scale

From: Felipe Gonçalves Assis
Subject: Re: Use of ly:set-default-scale
Date: Mon, 20 Dec 2010 13:34:44 -0300

Thanks Han-Wen!

2010/12/20 Han-Wen Nienhuys <address@hidden>:
> 2010/12/20 Felipe Gonçalves Assis <address@hidden>:
>> 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/ and
>> lily/, 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?
> Yes.  After setting the scale, you have to redefine the pitches for
> them to pick up the new scale.
>> 2. Is it a bug?
>> 3. Do we really have a problem with garbage collection?
>>    (I observe no consequences)
> No.  Since old pitches still have references to the old scale, it is
> not flushed.
>> 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.
> In general, I tried to avoid creating global variables (such as
> scale), as a matter of habit.
> --
> Han-Wen Nienhuys - address@hidden -

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