rfcs/docs/types-library-optional.md

types.optional

Summary

This RFC proposes adding a new method to the types library in type functions, that provides a shorthand for types.unionof(type, types.singleton(nil)).

Motivation

Optional types occur very commonly, and it is annoying to have to always type types.unionof(meow, types.singleton(nil)) to make a optional type, this leads to having the following appear in codebases that make use of optional types a lot in type functions:

type function optional(type)
	return types.unionof(type, types.singleton(nil))
end

Design

As a solution, a new method to the types library should be added called optional. When called on a union, this will add nil to the components. Otherwise, this new method will act the same as types.unionof(type, types.singleton(nil)).