Ever find yourself deep in some code, wishing that you could figure out if a gem was installed, without trying to call against it and deal with the ensuing nastyness? Here’s how:

dependency = Gem::Dependency.new "authlogic", ">2"
specs = Gem.source_index.search dependency
puts "the gem is not installed" if specs.empty?

Thanks to rubygems-sing for the simple implementation.

I wrote a piece of code recently to follow a linked list. We were linking records together in a way that a few records would normally be grouped together in a tree, with one parent above them all. However, because of the way the records were linked, it was also possible for a loop to occur — that is A would reference B, B would reference C, and C would reference A.