On April 13 2004, the patent "Extensible and efficient double dispatch in single-dispatch object-oriented programming languages" was issued to InternationalBusinessMachines in the UnitedStates.  The'' 'inventor' '' was JohnVlissides.

The patent describes a method, which involves a specific application of the VisitorPattern, of implementing DoubleDispatch in a SingleDispatch ObjectOrientedProgrammingLanguage.

See http://www.patentstorm.us/patents/6721807.html

''Somebody will patent *all* the GOF patterns, and then everyone will have to use procedural/relational instead. Bwaaa haa ha haa ha. -Tevilmind''

Or better yet, will have to ''go functional'' with languages that support true multi-dispatch.  Now where is Vlissides' god now?  :-) --SamuelFalvo
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Isn't this patent almost identical to the staggered Visitor approach described in PatternHatching (see VisitorInFrameworks for example)?  If not, then what is the innovation?  Surely JohnVlissides isn't patenting something he's already published!

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See SoftwarePatents

This is what permitting patents on software leads to- patents on software.