How to write an interface represents a tuple type in TypeScript?

Question

Glad to see the release of TypeScript 1.3, but how to write an interface represents a tuple type?

E.g.

var data: [string, number, number];

How to write an interface IData so that I would be able to do the same thing by writing

var data: IData;

Answer 1

I know this is an old question, but I think you can accomplish what you want with the following:

type IData = [string, number, number]; 

then

var data: IData; 

You can see this in this TypeScript Playground example

Answer 2

Note that with some of the new features coming, such as union types, you can get roughly what you want. The latest draft of the spec contains an example along these lines (see https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.3.3 )

The below code shows an example of how this might look:

interface KeyValuePair extends Array<string | number> { 0: string; 1: number; }

var x: KeyValuePair = ["test", 42]; // OK
var y: KeyValuePair = [42, "test"]; // Error

If you grab the latest code from the master branch and compile the above, you'll see where it detects the assignment to 'x' as valid, and the assignment to 'y' as an error:

S:\src\TypeScript\bin>node tsc c:\temp\tuple.ts
c:/temp/tuple.ts(4,5): error TS2323: Type '[number, string]' is not assignable to type 'KeyValuePair'.
  Types of property '0' are incompatible.
    Type 'number' is not assignable to type 'string'.

Answer 3

Little Late, but I think this approach is quite nice and simple and could help others:

type Type<T> = T;

interface IData extends Type<[number, number, number]>
{

}

var data: IData = ["Some Data", 42, 42];

This works also with Objects, if someone needs it:

type Type<T> = T;

interface IData extends Type<{ data: string }>
{

}

var data: IData = { data: "Some Data" };

You can also do this:

interface IData
{
    0: string;
    1: number;
    2: number;
}

var data: IData = ["Some Data", 42, 42];