Posted Jan 24, 2013 19:57 UTC (Thu) by jimparis (subscriber, #38647)
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That expression is true if "t" is a type, and fails to compile if "t" is a number, which is the main error that they were trying to catch. It also handles various other cases like passing an array type, see http://marc.info/?l=linux-kernel&m=106297035619199&... and subsequent messages.