Where do I find the new Span<T>?

You need to install prerelease version (check "Include prerelease" checkbox in nuget manager) of System.Memory package. Then just use Span (it's in System namespace).

Visual Studio 2019: If you are using the full .NET Framework (e.g. 4.7.2):

1. Go to NuGet packagemanager
2. Search for System.Memory package by Microsoft and install it.

Now you will be able to use Span<T>.

No need to search for pre-release versions anymore.