Is it possible to combine members of multiple types in a TypeScript annotation?

Question

It seems that what I am trying to do is not possible, but I really hope it is.

Essentially, I have two interfaces, and I want to annotate a single function parameter as the combination of both of them.

interface ClientRequest {     userId:     number     sessionKey: string }  interface Coords {     lat:  number     long: number } 

And then, in the function, I want to do something like this:

function(data: ClientRequest&Coords) { ... } 

So that my 'data' object could contain all of the members from both types.

I saw something referenced in a spec preview, under "Combining Types' Members", but it seems like this hasn't made it in yet.

If it isn't possible, my solution might look like this:

interface ClientRequest<T> {     userId:     number     sessionKey: string     data?:       T }  function(data: ClientRequest<Coords>) { ... } 

Which would work in this case, although it's not as dynamic as I would like. I would really like to be able to combine multiple (2+) types in the annotation itself:

function(data: TypeA&TypeB&TypeC) { ... } 

I would guess that the conventional solution is to define a type that extends those types, although that seems less flexible. If I want to add a type, I would have to either

• (a) go back to the declaration and rewrite it, or
• (b) create an entirely new interface. Not sure I agree with the extra overhead.

Any TypeScript experts care to point me in the right direction?

Answer 1

The specific answer to your question is: no, there is not a single inline annotation to signify combined or extended types.

The best practice for the problem you are trying to solve would be to create third type that would extend the other two.

interface IClientRequestAndCoords extends IClientRequest, ICoords {}   function(data: IClientRequestAndCoords)  

UPDATE 2018-10-30

TypeScript now has type intersections. So you can now simply do:

interface ClientRequest {   userId:     number   sessionKey: string }  interface Coords {   lat:  number   long: number }  function log(data: ClientRequest & Coords) {    console.log(     data.userId,     data.sessionKey,     data.lat,     data.long   ); }