Re: Implement \once as music function able to operate on complex stuff. (issue 5322065)

[reinhold . kainhofer]

http://codereview.appspot.com/5322065/diff/3001/input/regression/complex-once.ly
File input/regression/complex-once.ly (right):

http://codereview.appspot.com/5322065/diff/3001/input/regression/complex-once.ly#newcode11
input/regression/complex-once.ly:11: \unHideNotes  g a  \once\hideNotes
b c |
While this is the easy approach, it builds on the fact that hideNotes is
internally implemented as a music expression with several \override
commands. If that internal representation ever changes, we won't have a
proper regtest any more...
I would prefer to define the multiple property operations command
explicitly in the regtest, so we have complete control and no risk that
a totally unrelated change might break a regtest (without us even
noticing).

I.e. I would explicitly do
multipleOperations = {
  \override #'NoteHead #'color = #red
  \override #'Stem #'color = #blue
}

and then \once\multipleOperations.

http://codereview.appspot.com/5322065/