Re: gperl_type_get_property() default on unichar prop

[Torsten Schoenfeld <kaffeetisch gmx de>]

Kevin Ryde wrote:
> The program below gets a warning
>
>     Argument "\x{78}" isn't numeric in subroutine entry at foo.pl line 19.
>
> I think it's because in get_default_property_value() the call out to
> Glib::Param::Unichar::get_default_value() gives back a single-char
> string 'x' but gperl_value_from_sv() used on that return expects a
> number.

Hmm, tricky.  The problem seems to be that there is a mismatch between the type 
of the param spec (G_TYPE_PARAM_UNICHAR) and the GType used to store and marshal 
values of it (G_TYPE_UINT).  When we have the Glib::Param::Unichar object, we 
know it's a unichar.  But when we are dealing with values for properties 
described by this param spec, we don't have this knowledge and instead only know 
that we deal with a uint.

> I'd be sorely tempted to say Glib::Param::Unichar::get_default_value()
> is the odd man out and ought to be returning a number the same as
> $obj->get_property or $obj->set_property give and return for a unichar
> prop.  But would changing that break anyone's program?

I think Glib::Param::Unichar::get_default_value() doesn't look so odd anymore 
when you consider that it simply uses the gunichar typemap.  Every other xsub 
that returns or takes a gunichar automatically uses the same one-character 
string representation.

Changing Glib::Param::Unichar::get_default_value() to return a plain number 
would break users that directly call it.

> The other temptation would be to switch get_default_property_value() to
> using g_param_value_set_default(), since that latter does the right
> thing on unichar pspecs.  But would anyone have their own subclassed
> $pspec->get_default_value() which would be lost by using only
> g_param_value_set_default() ?

I don't know.  The current get_default_property_value() certainly allows custom 
param specs to provide their own get_default_value() and have it called when 
appropriate.

The only possible solution that comes to mind is to attack this at the only 
place that sees both the GParamSpec and the GValue: 
get_default_property_value().  Maybe it could, upon a seeing a param spec of 
type G_TYPE_PARAM_UNICHAR, mangle the SV returned by 
Glib::Param::Unichar::get_default_value() before passing it to 
gperl_value_from_sv()?

-Torsten