Re: Class::Interface -- isa() Considered Harmful

You don't need isa, you need can.

I often write code of which I assume that an object is able to execute certain methods. When in doubt, I try can() first, before actually calling the method. These classes do not need to be derived from a common class, that is an implementation detail to make virtual classes possible in languages like C++, for example. In Perl, when classes don't have common methods, it doesn't make sense to make them inherit from a common ancestor class.

I do assume that for those classes, methods of the same name serve a similar purpose, and have the same API. That may be a weak point. Likely so.

Comment on Re: Class::Interface -- isa() Considered Harmful

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Re: Re: Class::Interface -- isa() Considered Harmful by dws (Chancellor) on Jan 16, 2003 at 07:37 UTC
You don't need `isa,` you need `can.` An interface is a contract. Having a method with a given name isn't. Keeping the conversation at the level of "will this object honor a given contract" (i.e., `isa`) is preferable to risking false positive based on method names. A baseball player and an airplane both know about "pitch", but the meanings are entirely different.	[reply] [d/l] [select]
Re: Re: Class::Interface -- isa() Considered Harmful by chromatic (Archbishop) on Jan 16, 2003 at 07:42 UTC
You're right that `can()` is a better approach for protecting against methods that aren't there. I'm working on something at a higher level, though. For example, you don't have to check `can()` all the time. If you're handed an object, check that it implements the appropriate interface, then keep it around. With interfaces, for example, it's easy to mixin a batch of methods from another class -- marked as an interface.	[reply] [d/l] [select]


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