def self.for(requirement)
ranges = requirement.requirements.map do |op, v|
case op
when "=" then ReqR.new(ReqR::Endpoint.new(v, true), ReqR::Endpoint.new(v, true))
when "!=" then NEq.new(v)
when ">=" then ReqR.new(ReqR::Endpoint.new(v, true), ReqR::Endpoint.new(ReqR::INFINITY, false))
when ">" then ReqR.new(ReqR::Endpoint.new(v, false), ReqR::Endpoint.new(ReqR::INFINITY, false))
when "<" then ReqR.new(ReqR::Endpoint.new(ReqR::ZERO, true), ReqR::Endpoint.new(v, false))
when "<=" then ReqR.new(ReqR::Endpoint.new(ReqR::ZERO, true), ReqR::Endpoint.new(v, true))
when "~>" then ReqR.new(ReqR::Endpoint.new(v, true), ReqR::Endpoint.new(v.bump, false))
else raise "unknown version op #{op} in requirement #{requirement}"
end
end.uniq
ranges, neqs = ranges.partition {|r| !r.is_a?(NEq) }
[ranges.sort_by {|range| [range.left.version, range.left.inclusive ? 0 : 1] }, neqs.map(&:version)]
end