notes.md

Overview of type categories and usage

	reference type	nullable reference type	value type	nullable value type	unspecified
ctor/method parameter	T	T?	T	T?	T?
field	T	T?	T	T?	T?
typecasting	T	T?	T	T?	T?
type category constraint	class	class?	struct	N/A	default
nullability constraint	notnull	N/A	notnull	N/A	-
typeof	typeof(T)	N/A	typeof(T)	typeof(T?)	-

Implementing Either

Since Either is a choice monad, we need to store values in "nullable" fields. That means that we still use ? for reference type with notnull constraint. Only case where we may want to omit ? is for non-nullable struct.

Passing current value

Consider value is stored in _v1 field (and we use T? for type - since we don't know in which state monad is):

type category	nullability	referencing field	description
reference	notnull	_v1!	we need to use null forgiving operator (!)
reference	nullable	_v1	value may be null, no need for !
value	notnull	_v1	value is struct, no need for !
value	nullable	_v1	value is struct Nullable<T>, no need for !

Implementing Either.TryPick

Consider value is present and we call TryPick method:

type category	nullability	method signature	description
reference	notnull	bool TryPick([NotNullWhen(true)] out T? value)	if we pick value, we know that value is not null
reference	nullable	bool TryPick(out T? value)	value may be null
value	notnull	bool TryPick(out T value)	value is struct, can't be null
value	nullable	bool TryPick(out T? value)	value is struct Nullable<T>, can't be null

Handling nullable reference type scope

	#nullable enable	#nullable disable	description
non-nullable ref type	T	N/A	There's no way how to mark type non-nullable if null-ref types is disabled
nullable ref type	T?	T	If null-ref type is disabled, all reference types are possibly null
value type	T	T
nullable value type	T?	T?