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Implement Linq CountBy method for IEnumerable and IQueryable #91507

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merged 8 commits into from
Sep 14, 2023
Merged

Implement Linq CountBy method for IEnumerable and IQueryable #91507

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8acd0ca
Implement Linq CountBy method for IEnumerable
manandre Aug 23, 2023
4d54545
Implement Linq CountBy method for IQueryable
manandre Aug 24, 2023
b7ba647
Remove useless using statement
manandre Aug 24, 2023
356482d
Lazy source enumeration
manandre Sep 4, 2023
c50ad74
Avoid useless allocation when source is empty
manandre Sep 12, 2023
6e3c6d4
Rename with CountByIterator and avoid local methods
manandre Sep 13, 2023
86fef12
Add tests around lazy enumeration
manandre Sep 13, 2023
256f96a
Make test results more explicit
manandre Sep 13, 2023
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30 changes: 30 additions & 0 deletions src/libraries/System.Linq/tests/CountByTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,36 @@ public void CountBy_KeySelectorNull_ThrowsArgumentNullException()
AssertExtensions.Throws<ArgumentNullException>("keySelector", () => source.CountBy(keySelector, new AnagramEqualityComparer()));
}

[Fact]
public void CountBy_SourceThrowsOnGetEnumerator()
{
IEnumerable<int> source = new ThrowsOnGetEnumerator();

var enumerator = source.CountBy(x => x).GetEnumerator();
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Assert.Throws<InvalidOperationException>(() => enumerator.MoveNext());
}

[Fact]
public void CountBy_SourceThrowsOnMoveNext()
{
IEnumerable<int> source = new ThrowsOnMoveNext();

var enumerator = source.CountBy(x => x).GetEnumerator();

Assert.Throws<InvalidOperationException>(() => enumerator.MoveNext());
}

[Fact]
public void CountBy_SourceThrowsOnCurrent()
{
IEnumerable<int> source = new ThrowsOnCurrentEnumerator();

var enumerator = source.CountBy(x => x).GetEnumerator();

Assert.Throws<InvalidOperationException>(() => enumerator.MoveNext());
}

[Theory]
[MemberData(nameof(CountBy_TestData))]
public static void CountBy_HasExpectedOutput<TSource, TKey>(IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IEqualityComparer<TKey>? comparer, IEnumerable<KeyValuePair<TKey, int>> expected)
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