Re: get_property vs internal_get_property (was: issue 127860043)

[Mike Solomon]

On Aug 18, 2014, at 9:39 AM, Janek Warchoł <address@hidden> wrote:

> Hi,
> 
> it's time to ask a n00b question and get the elephant (that was
> bothering me for a couple years) out of the room: why do we have - and
> use! - both get_property and internal_get_property?  We ought to use
> get_property everywhere, right?
> 
...
> 
> We are also converting property names from strings to symbols
> everywhere - for example
> 
> SCM meta = info.grob ()->internal_get_property (ly_symbol2scm ("meta"));
> 
> What's the reason for that?  And shouldn't we write all the C++ code
> so that it will automatically do the conversion, like get_property
> does?
> 

Entirely reasonable and good idea!
The only slight annoyance is that it is backwards from the logic of almost all 
other “internal_X" patterns in LilyPond, where the function X takes Scheme 
values and "internal_X" takes C++ values.

Cheers,
MS

> Whew.  I feel like an idiot now.
> 
> best,
> Janek
> 
> 
> 2014-08-18 8:09 GMT+02:00  <address@hidden>:
>> 
>> https://codereview.appspot.com/127860043/diff/40001/lily/lily-guile.cc
>> File lily/lily-guile.cc (right):
>> 
>> https://codereview.appspot.com/127860043/diff/40001/lily/lily-guile.cc#newcode201
>> lily/lily-guile.cc:201: robust_scm2bool (SCM b, bool def)
>> On 2014/08/18 04:57:08, Keith wrote:
>>> 
>>> I am not sure, but I think this is a bad idea.
>>> to_boolean() is robust to undefined symbols, returning #f, and a lot
>> 
>> of
>>> 
>>> define-grobs.scm depends on that convention.
>>> If you add this variant, and people start writing C++ that treats
>> 
>> undefined
>>> 
>>> symbols as #t, we might get confused.
>> 
>> 
>> Hmm.  Good point.  However, to me the situation without robust_scm2bool
>> is also confusing: in fact, i was confused enough to write buggy code :(
>> As far as i can see, the code for getting non-boolean properties
>> follows the convention:
>> 
>> Type value = robust_scm2type (grob->get_property("prop-name"), default)
>> 
>> When writing code for issue 2245, I have initially tried to use
>> robust_scm2bool - which didn't exist.  As i was not aware of to_boolean,
>> i ended up with ly_scm2bool, which turned out to be a bad choice.
>> 
>> So, my question is: can we do something to make this more intuitive?
>> 
>> What about writing utility functions for getting and converting
>> properties in one step?  The current situation is not very elegant - the
>> code sometimes gets so long that it's hard to fit it in 80 chars limit.
>> 
>> https://codereview.appspot.com/127860043/
> 
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