[Bioperl-l] attribute setting and return value

[Steve Chervitz]

This is yet another "gotcha" that arises from having combined set/get
accessors. It's convenient sure, but not so clean from an engineering point of
view since it relies on a shared convention. 

I can't say I've never done anything with the return value from a set
operation, but I don't normally rely on it. So IMHO, I'd recommend declaring
that, unless it's explicitly documented in the method's POD, the return value
from a set operation on a combined accessor is not specified and should not be
used by the faint of heart.

Steve

--- Hilmar Lapp <hlapp@gnf.org> wrote:
> While I tried to investigate a test failure in Lincoln's BioGraphics 
> I noticed a somewhat important style difference between bioperl and 
> Lincoln's:
> 
> When we set an attribute, we always return the value that was just set:
> 
>      sub my_attribute{
>          my ($self,$value) = @_;
>          $self->{'attrkey'} = $value if defined $value;
>          return $self->{'attrkey'};
>      }
> 
> In Lincoln's style, the _previous_ value is returned (which in many 
> cases will be undef!):
> 
>      sub my_attribute{
>          my ($self,$value) = @_;
>          my $v = $self->{'attrkey'};
>          $self->{'attrkey'} = $value if defined $value;
>          return $v;
>      }
> 
> Lincoln, I'm just second-guessing that after having seen this in 
> multiple getter/setters, that it is probably your preferred style. 
> If this is confined to only a few or one module, then my point is 
> almost moot (but maybe still worth mentioning).
> 
> These styles are inconsistent with each other, and if an interface 
> is implemented in different styles (which is the case for e.g. 
> Bio::SeqFeatureI in Bio::SeqFeature::* and Bio::Graphics::*), the 
> returned values will not be the same, and also not comply with the 
> interface definition.
> 
> It is going to be very hard to change this all over bioperl ... (I 
> guess it also hard to change this all over Bio::Graphics ...) (I 
> certainly do not want to rate the merits of one against the other 
> here -- to me both styles make a lot of sense)
> 
> I don't think that anyone takes advantage yet of using the returned 
> value when setting an attribute (speak out if you do). Maybe the 
> sensible thing to do in order to prevent future havoc is to advise 
> people not to rely on the returned value when setting an attribute.
> 
> Lincoln/Ewan/Jason/Heikki, any thoughts on this or votes?
> 
> 	-hilmar
> 
> --
> -------------------------------------------------------------
> Hilmar Lapp                            email: lapp at gnf.org
> GNF, San Diego, Ca. 92121              phone: +1-858-812-1757
> -------------------------------------------------------------
> 
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=====
Steve Chervitz
sac@bioperl.org

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