I also wish 'sealed' was the default for classes in templates. Usually you're not thinking about what will happen if someone shows up 5 years later to derive fr

I also wish 'sealed' was the default for classes in templates. Usually you're not thinking about what will happen if someone shows up 5 years later to derive from a random class you created, and it has performance benefits to seal a type. You can always remove the sealed qualifier later on purpose.