In my code, there is a function named isDone() that will return data from either an array of hashes or a dictionary of hashes:
public async isDone() {
this.startDelayedTasks();
await Promise.all(this._tasks);
const hadErrors = this._failed.length > 0 ? true : false;
if (hadErrors) {
throw new ParallelError(this);
}
return this._resultType === "hash"
? (this._results as IDictionary<T>)
: hashToArray<IParallelArrayType<T>>(this._results) as IParallelArrayType<T>[];
}
The interface for IParallelArrayType looks like this:
export interface IParallelArrayType<T> {
name: string;
value: T;
}
If consumers request the array type, they might want to use functions like map, filter, or length. However, since the return type could be different, it can lead to errors like this:
https://i.sstatic.net/0Lvhl.png
To work around this issue, consumers can add a check like this:
if(Array.isArray(results)) {
expect(results.length).to.equal(4);
}
It would be helpful if there was a way to avoid burdening the consumer with handling this. One idea could be implementing a tagged union type and using a Symbol for identifying the property.
This approach seems promising, but I also want to make sure that consumers of the hash/dictionary return type do not see the Symbol key when iterating through the object using Object.keys(dictionary). Is there a solution to achieve this, or am I delving too deep into the runtime environment?