Func<ReadOnlySpan<char>,bool> to do some work in helping me parse, which would take in the Span to do some work. However, this is illegal in C# Compiler Error CS0306 due to ReadOnlySpan<char> being a pointer type readonly ref struct. I have considered just making a type, with one function on it, and overriding that in subtypes to get around it, but this is really not suitable. I may for instance wish to compile LINQ expressions at run time, to server as parsers.