Intersect

[isc30]

Produces the set intersection of two sequences (deferred execution)

Proposed signature:

export interface IQueryable<TOut>
{
    intersect(other: IQueryable<TOut>): IEnumerable<TOut>;
}

[nikolalukovic]

I suppose we will also need to have something like an EqualityComparer to specify in which way to compare values?

We would have an optional value which would specify in which way to do an intersection. Something like this?

export interface IQueryable<TOut>
{
    intersect(other: IQueryable<TOut>, comparer?: EqualityComparer<TOut>): IEnumerable<TOut>;
}

Maybe it would also be a good idea to create comparers for simple types(string, number, etc...) which would be automatically used(depending on the type) if no comparer is specified.

[isc30]

The only place where comparers are being used currently is for orderBy, maybe it's a good idea to introduce a StrictEqualityComparer that simply does === and start using it here as default one?

We can introduce something like this:

export type EqualityComparer<T> = (left: T, right: T) => boolean;
export const StrictEqualityComparer = <T>() => (left: T, right: T) => left === right;

[nikolalukovic]

It all depends how precise you want to go. I'd argue that for strings, as an example, being careful about locale is a must. And === doesn't help in that case.

[isc30]

yep, but in the end, having special comparer for those cases is user's responsibility.
I think the best we can do is use === as default (every other method in the library uses this comparer)
I also edited my previous answer

[Tholdrim]

Since EqualityComparer is there already, I'll grab this task.