Re: [Module::Build] version.pm and version number comparison problem

[Ken W. <ke...@ma...>]

On Feb 2, 2006, at 10:52 PM, Chris Dolan wrote:

> On Feb 2, 2006, at 10:26 PM, Ken Williams wrote:
>
>> On Feb 2, 2006, at 10:18 PM, Chris Dolan wrote:
>>> Well, if it throws an exception, it's probably not a version 
>>> instance, right?
>>
>> Why not?  It could be a version instance that overloads isa() for 
>> whatever satanic purpose it wants to, and throws an exception, 
>> because it's evil and it can.
>
> I don't think version.pm is actually in league with the devil. :-)

I was referring to some possibly strange & unknown class that 
subclasses version.pm.

> Presumably, version would only override isa() if it really, really 
> needed to be overridden.  Why should we ignore that decision that was 
> probably made with great care?

Because IMO even if it was made with great care it's wrong.  You can't 
change perl's notion of what constitutes a subclass even if you do 
override isa().

As I published in a review of UNIVERSAL::isa() last night, this is very 
different from overriding can().  For can(), the author does have the 
ability to override perl's dispatch of method calls via AUTOLOAD(), so 
overriding can() is a good idea.  For isa(), we can't override perl's 
OO inheritance notions, so overriding isa() is a bad idea and will 
leave the caller in a state of confusion over who's right, perl or 
isa().


> No, that's not right.  What you want to know is if the $version is not 
> a plain scalar and therefore whether it needs to be numify()ed.  
> isa('version') is a close proxy for that decision.

Just because it's not a plain scalar, though, doesn't mean it needs to 
be numified.  Theoretically someone has written their *own* class for 
version objects, independent of version.pm, which they think is going 
to handle things their own special way without use of a numify() 
method.

In this case we really *do* want to know whether the $version inherits 
from version.pm, because then it will have a published numify() method 
with known semantics.  If it's some other class, we know nothing.

  -Ken