1.0.2 • Published 7 years ago
flow-classy-type-wrapper v1.0.2
Classy Type-Wrapper for Flow
A tiny module that gives you the TypeWrapper
class + static methods bundle, for quick definition of type wrappers.
What are Type Wrappers?
A way of declaring a new type, that is simply a wrapper around another type, to make mix-ups easier to prevent. For example, declaring a wrapper around string
called UserID
, to stop User IDs from being mixed up with other strings, like usernames or descriptions.
This is elaborated on in this blog post.
Usage
// @flow
import { TypeWrapper } from 'flow-classy-type-wrapper';
// Declare a new type wrapper:
class UserID extends TypeWrapper<string> {}
// String -> UserID-wrapped String
const id = UserID.wrap("123-abcd");
// $ExpectError - Can't use like a string without unwrapping.
const wrong = "Hello, user #" + id;
function greet(userId: UserID, name: string): string {
// UserID-wrapped String -> String
const userIdAsString = UserID.unwrap(userId)
// Unwrapped; fine to use now.
return "User #" + userIdAsString + ": " + name;
}
console.log(greet(id, "Bert"));
See the examples/
directory for more.
Inspired by @mkscrg's original "class bundle" pattern from this Flow issue.