I'd personally rather say "Make sure this object can handle any message I can send an Arcade." Since the Airport contains an Arcade, it will just delegate methods like colle­ct_qu­arter­s and play_­annoy­ing_d­ance_­music to the Arcade it contains.
Why should an Airport act as an Arcade?

As an example, let's pretend a mall has a skate park in it. I don't think that the mall should act as a skate park in any way--unless you're writing a Tony Hawk game. :^)

Going back to interfaces, the one thing I see them as being useful for in a language that supports MI is for specifying properties of a class (in the Perl 6 sense of the word). For example, in .NET any serializable class implements the ISerializable interface. (I've probably got some karmic justice coming soon for suggesting that an M$ design is good... ;^) )

Personally, I would standardize on a 'get_arcade' method for when you're handed something that isn't an Arcade: 

$arcade=$arcade->get_arcade until $arcade->isa('Arcade');

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--Brent Dax
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In reply to Re: Class::Interface -- isa() Considered Harmful by BrentDax
in thread Class::Interface -- isa() Considered Harmful by chromatic

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