Why can't TypeScript modules implement or adhere to an interface? Can I get around this?

Question

It seems like it would be very useful in TypeScript to require that a module implement an interface. Is there any particular reason why they've chosen to not implement this ability?

I can't think of any reason why it would be undesirable to allow a module implement an interface, but if it is, then is there any other way to require a module provide a certain set of properties / methods?

Answer 1

You can force a compile error if a module doesn't adhere to an interface like this (technically non-zero runtime overhead, but unlikely to actually matter):

interface foo {
    bar(): number;
}

module mod {
    export function bar(): number {
        return 0;
    }
}
var mod_is_foo: foo = mod; // errors if you change 'number' to 'string' above

As for why can't you say module mod implements foo? All features start at minus 100.

Edit to add -- here are some other (somewhat wacky) things you could write in lieu of the var statement above if you wanted to avoid creating a new top-level var:

<foo>mod; // Shortest, probably fastest?
<foo>undefined === mod; // Clearest non-var version?