Re: override ?

[Thomas Morley]

Am Mo., 23. Dez. 2019 um 21:40 Uhr schrieb Freeman Gilmore
<address@hidden>:
>
> Would someone explain what line 5 does and what  "::"means?   Why line 6 is 
> not enough.
>
> 1 \version "2.19.10"
> 2 sesquisharp = \markup { \sesquisharp }
> 3
> 4 \relative {
> 5    \once \override Accidental.stencil = #ly:text-interface::print
> 6    \once \override Accidental.text = #sesquisharp
> 7    cis''4 }
>
> Thank you, ƒg

The default stencil-procedure to print Accidental is
`ly:accidental-interface::print`. It does _not_ read the text-property
Line 5 changes the procedure to `ly:text-interface::print`, which does
read said text-property.
Thus you need both if you want to go this route.

Although, this method is documented, it's implementation is a lil bit so-so.
If you complie with the option `-dcheck-internal-types` you'll get:
programming error: Grob `Accidental' has no interface for property `text'
continuing, cross fingers

The "::" is more a convention, you'll find a plethora of namings
containing them, mostly call-backs.
You could change it:

\version "2.19.10"

sesquisharp = \markup { \sesquisharp }

#(define text-interface-print ly:text-interface::print)

\relative {
   \once \override Accidental.stencil = #text-interface-print
   \once \override Accidental.text = #sesquisharp
   cis''4 }

Cheers,
  Harm