I&#x27;m assuming you&#x27;re talking about heterogenous collections, which while totally possible with powerful static type systems, I&#x27;d consider not to be a great idea. If even <i>I</i> don&#x27;t know what&#x27;s in my collections <i>now</i> (if I knew I could model it in the type system – it takes 30 seconds at most), how on Earth is my successor going to know in six months time? Heterogenous collections are a maintenance nightmare. I have only ever seen them used in a way where they should be refactored first thing in the morning.