On Sat, 2009-11-21 at 17:22 +0100, David Kastrup wrote: > There is a chapter "set vs override" in the manual. > > I am afraid that I fail to grasp the difference from the chapter. > > It says: "There are actually two different kinds of properties." > > But then it says > > Context properties can change value over time while interpreting a > piece of music; `measurePosition' is an obvious example of this. > Context properties are modified with `\set'. > > So far so good. > > There is a special type of context property: the element > description. > > If the element description is a _special_ type of context property, that > would imply that there is just _one_ different kind of properties. It > completely fails to mention _what_ makes the element descriptions > special and not settable with \set. > > These properties are named in `StudlyCaps' (starting with capital > letters). They contain the `default settings' for said graphical > object as an association list. See `scm/define-grobs.scm' to see > what kind of settings there are. Element descriptions may be > modified with `\override'. > > So why can't we use \set with element descriptions? And where is the > difference to context properties changing values? After all, the > principal purpose of \override is also to change the value, and > \once\override very obviously changes behavior over time while > interpreting music.
Since \override works by modifying special context properties, you can actually use \set for setting grob properties. However, \override does some extra useful work: for a start, it appends new overrides to a list of overrides for a grob so that they can be easily reverted (\set just clobbers the existing variable). Also, \override supports nested properties (useful for things like 'bound-details). The type-checking mechanisms are also different for \override and \set. The implementation of \override is in context-property.cc, if you want to look at it. Cheers, Joe _______________________________________________ lilypond-user mailing list lilypond-user@gnu.org http://lists.gnu.org/mailman/listinfo/lilypond-user
