Proposal: Spread Interface Operator

Suggestion

When we want to extend a interface we use the "extends" keyword. So for example:

interface Foo {
   keyA: string,
   keyB: number,
}

interface ExtendsFoo extends Foo {
    keyC: any
}

My idea is to define the same interface ExtendsFoo but using what I would call the Spread Interface Operator.

The code mentioned above could be rewritten as:

interface Foo {
   keyA: string,
   keyB: number,
}

interface ExtendsFoo {
   ...Foo,
   keyC: any
}

I think this could be another way of expressing types that reminds spread operator syntax in Javascript.

The proposal concerns TypeScript interface inheritance and JavaScript spread syntax. Start by reviewing how existing interface and extends syntax is specified and parsed, then determine the design implications of allowing spread members in interfaces. Done would require an accepted language design plus implementation and conformance coverage.