What is the correct way to specify type hints for a Stream of Streams in highlandjs?

I'm currently working with typescript@2 and the highlandjs library. In the typings for highland, there seems to be a missing function called mergeWithLimit(n). This function:

Accepts a Stream of Streams, merges their values and errors into a single new Stream, and limits the number of unpaused streams that can run at any given time.

Unfortunately, this method has not been typehinted yet in the DefinitelyTyped typings. I attempted to add it, but there is only an interface Stream<R> and none for a stream of streams.

How can I create an interface for a stream of streams? I tried defining an interface:

interface Stream<Stream<R>> implements Stream<R> {
    mergeWithLimit(n: number): Stream<R>;
}

However, it does not compile:

365     interface Stream<Stream<R>> implements Stream<R> {
                               ~

index.d.ts(365,28): error TS1005: ',' expected.


365     interface Stream<Stream<R>> implements Stream<R> {
                                  ~

index.d.ts(365,31): error TS1109: Expression expected.


365     interface Stream<Stream<R>> implements Stream<R> {
                                               ~~~~~~

index.d.ts(365,44): error TS1005: ';' expected.

What is the correct way to typehint mergeWithLimit?

genericstypescripttypescript-typingshighland.js

Answer №1

We successfully implemented type hinting by creating an interface:

interface CollectionOfCollections<T> extends Collection<Collection<T>> {
    /**
     * This method takes a collection of collections and combines their elements into a single new Collection,
     * limiting the number of active collections that can run concurrently.
     *
     * @id combineWithLimit
     * @section Collections
     * @name Collection.combineWithLimit()
     * @api public
     */
    combineWithLimit(limit: number): Collection<T>;
}

In addition, we defined a map function as follows:

interface Collection<T> extends EventTarget {
    map<U>(func: (item: T) => U): Collection<U>;
    map<S>(func: (item: T) => Collection<S>): CollectionOfCollections<S>;
}

Now we are able to apply correct type hinting to combineWithLimit(limit) using the following syntax:

myCollection.map<YourType>(mapFunction).combineWithLimit(5)

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