CODEWITHSUNDEEP
typescript
monnef
monnef

Reputation: 4053

How to create an extendable type via Partial without duplicating code?

Let's have following code:

interface A {
  a: number;
}

// doesn't work - "An interface may only extend a class or another interface."    
// interface AOpt extends Partial<A> {} 

// does work, but leads to code duplication :(
interface AOpt {
  a?: number;
}

interface B extends AOpt {
  b: number;
}

How to create an interface in a way Partial works with type, but so it is extend-able by an interface?

Upvotes: 5

Views: 1171

Answers (1)

Paleo
Paleo

Reputation: 23702

It seems our needs will be covered by the next release of TypeScript, with the pull request "Allow deriving from object and intersection types":

type T1 = { a: number };
type T2 = T1 & { b: string };

// ...

type Named<T> = T & { name: string };

interface N1 extends Named<T1> { x: string } // { a: number, name: string, x: string }
interface N2 extends Named<T2> { x: string } // { a: number, b: string, name: string, x: string }

interface P1 extends Partial<T1> { x: string } // { a?: number | undefined, x: string }

In the roadmap, it appears under the label "Improved support for "mixin" patterns", which is checked. Therefore, it should be available in typescript@next.

Upvotes: 3

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