feat(assign): refine types

[crishoj]

Summary

The type declaration with assign (mistakenly?) requires that both arguments have the same shape.

Taking the example from the docs:

Two warnings:

After:

For any code change,

• Related documentation has been updated, if needed
• Related tests have been added or updated, if needed
• Related benchmarks have been added or updated, if needed

Does this PR introduce a breaking change?

No

[aleclarson]

Unfortunately, X & Y is not representative.

type A = {a: number}
type B = {a: string}

type C = A & B

declare const c: C
c.a // number & string

Link to above example in playground.

We actually want c.a to result in string (as string will always override number). If B["a"] was possibly undefined like {a?: string}, then c.a should result in number | string.

[crishoj]

You're right, A & B does not result in the desired type.

Perhaps something like the Merge TS helper from https://github.com/millsp/ts-toolbelt/blob/master/sources/Object/Merge.ts could work?

[aleclarson]

See comment ✌️

[aleclarson]

Thanks for the contributions, @crishoj!

I agree the current assign types are not good :)

[aleclarson]

Closed in favor of #142