On nullability and null checking

[dodexahedron]

Just a general comment for code in the project, when null checks are performed.

If you are explicitly checking for or against null, you should use either the is null or is { } patterns.

Why?

operator== can be overloaded. The is operator cannot. Therefore, the is operator will ALWAYS be a check against null, whereas x == null is not a guarantee, at the call site.

Plus, that comes with some syntactic goodies like being able to do a check and an assignment in one line, such as:

if(someNullableThing is SomeType x) {
  x.Method();
}

That's a null check and, if not null, assignment to x, for later use, at the same scope as the if statement (so not just within the brackets).

Just something to be aware of.

[dodexahedron]

And for argument validation, there are the ArgumentException.ThrowIfNull* helpers, as well.

[dodexahedron]

These, by the way, pre-wire up the stuff you'd otherwise have to give as parameters if throwing your own exception, such as the parameter name.

The only semi-sucky thing is they don't have overloads that allow custom messages, but I think the intent behind that was to standardize the experience for consumers, around ArgumentException and ArgumentNullException, so I'm mostly over it.