[API Proposal]: ExceptBy taking another collection of the source type

[weitzhandler]

Background and motivation

Please add an overload of ExceptBy that takes another collection of the source type (instead of TKey type). The same keySelector will then be used to obtain the keys from both collections.

Related #115797

API Proposal

namespace System.Collections.Generic;

public static class Enumerable
{
+    public static IEnumerable<TSource> ExceptBy<TSource, TKey>(
         this IEnumerable<TSource> first,
         IEnumerable<TSource> second,
         Func<TSource, TKey> keySelector);
}

API Usage

IEnumerable<Source> x = ...;
IEnumerable<Source> y = ...;

var excepted = x.ExceptBy(y, source => source.Key);

Alternative Designs

No response

Risks

No response

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[eiriktsarpalis]

IIRC such an overload was considered when we were reviewing the design. Ultimately it was decided to keep things simple since you can easily obtain the required behaviour by running a select on the second enumerable.

[weitzhandler]

I mean, we're already specifying the key selection here, why specify it twice.
To me, the proposed overload is more useful than the implemented one.