Re: ly:output-def-clone not working correctly?

[David Kastrup]

Thomas Morley <address@hidden> writes:

> 2017-10-08 13:36 GMT+02:00 David Kastrup <address@hidden>:
>>
>> I think using a different layout than the one your output appears in
>> is not a supported idea.  Output definitions are hemimetabolic.  They
>> may be an "output definition" but it's not like they are being used
>> to instantiate a separate "output" type like a context definition is
>> instantiated into a context.  Instead, output definitions may receive
>> the side effects from their uses (which include managing the writing
>> of a Midi/PDF file, and in this case, causing font definitions).
>
> Thanks for your explanations.
>
> In the german forum it was attempted to set 'line-width to some
> calculated value relying on the found 'line-width in layout. With
> multiple calls the found line-width will become the calculated one
> from the previous call not the original, thus the idea of cloning the
> layout, similiar to ly:music-deep-copy.
>
> Iiuc, you would say it's a not supported (in this case read: bad)
> idea.

Cloning outputs is fine before they become part of a score/book.  But
once you use them for turning markup into stencils, those stencils
should appear in the book/score using that output.

So in usage, there is sort of a distinction between an "output
definition" and an actual "output", but the data type is just the same.
Hemimetabolic.  There is a moment in its life time after which cloning
becomes a bad idea, somewhat depending on what you need the clone for.

-- 
David Kastrup