Re: Two arpeggio lines (up and down) next to each other

[Jean Abou Samra]

Le 12/10/2021 à 15:33, David Kastrup a écrit :
> but I don't even know whether there is a guarantee that
> ly:arpeggio::print is happy with the grob being modified after the call
> and before the stencil is getting used.  Looking at the C++ code, that
> appears to be the case.  Maybe giving ly:arpeggio::print an optional
> overriding direction argument could be cleaner?  It doesn't help with
> creating user-level code for current LilyPond versions, of course.


Properties can be accessed from anywhere, provided no cyclic
dependencies. If ly:arpeggio::print calls anything that also
needs the arpeggio's direction, that will be cached and screw up.
There are a number of bugs caused by evaluation of callbacks
at a wrong point in time when the property has not been set by
what was supposed to set it, and they are hell to track down
because it's not always clear how execution was supposed to happen
in the first place and sometimes things just worked by accident.
So even though there may be no problem in this specific instance,
I really don't think we would want to encourage this style of coding.

A solution to this particular problem might be allowing several
arpeggios in the same timestep.

Best,
Jean