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TagFirstLast: IList<> implementation #408

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merged 1 commit into from
May 10, 2023
Merged

TagFirstLast: IList<> implementation #408

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42 changes: 42 additions & 0 deletions Source/SuperLinq/TagFirstLast.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,9 @@ public static IEnumerable<TResult> TagFirstLast<TSource, TResult>(this IEnumerab
Guard.IsNotNull(source);
Guard.IsNotNull(resultSelector);

if (source is IList<TSource> list)
return new TagFirstLastIterator<TSource, TResult>(list, resultSelector);

return Core(source, resultSelector);

static IEnumerable<TResult> Core(IEnumerable<TSource> source, Func<TSource, bool, bool, TResult> resultSelector)
Expand All @@ -88,4 +91,43 @@ static IEnumerable<TResult> Core(IEnumerable<TSource> source, Func<TSource, bool
yield return resultSelector(cur, first, true);
}
}

private class TagFirstLastIterator<TSource, TResult> : ListIterator<TResult>
{
private readonly IList<TSource> _source;
private readonly Func<TSource, bool, bool, TResult> _resultSelector;

public TagFirstLastIterator(IList<TSource> source, Func<TSource, bool, bool, TResult> resultSelector)
{
_source = source;
_resultSelector = resultSelector;
}

public override int Count => _source.Count;

protected override IEnumerable<TResult> GetEnumerable()
{
if (_source.Count <= 1)
{
if (_source.Count == 1)
yield return _resultSelector(_source[0], true, true);
yield break;
}

yield return _resultSelector(_source[0], true, false);

var cnt = (uint)_source.Count - 1;

for (var i = 1; i < cnt; i++)
yield return _resultSelector(_source[i], false, false);

yield return _resultSelector(_source[^1], false, true);
}

protected override TResult ElementAt(int index)
{
Guard.IsBetweenOrEqualTo(index, 0, _source.Count - 1);
return _resultSelector(_source[index], index == 0, index == _source.Count - 1);
}
}
}
57 changes: 24 additions & 33 deletions Tests/SuperLinq.Test/TagFirstLastTest.cs
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Expand Up @@ -9,44 +9,35 @@ public void TagFirstLastIsLazy()
_ = new BreakingSequence<object>().TagFirstLast(BreakingFunc.Of<object, bool, bool, object>());
}

[Fact]
public void TagFirstLastEmptySequence()
{
using var sequence = TestingSequence.Of<int>();

var result = sequence.TagFirstLast();
result.AssertSequenceEqual();
}

[Fact]
public void TagFirstLastWithSourceSequenceOfOne()
public static IEnumerable<object[]> GetSourceSequences() =>
Enumerable.Range(0, 4)
.SelectMany(n =>
Enumerable.Range(0, n)
.GetListSequences()
.Select(x => new object[] { x, n }));

[Theory]
[MemberData(nameof(GetSourceSequences))]
public void TagFirstLastVaryingLengths(IDisposableEnumerable<int> seq, int n)
{
using var sequence = TestingSequence.Of(123);

var result = sequence.TagFirstLast((item, isFirst, isLast) => new { Item = item, IsFirst = isFirst, IsLast = isLast });
result.AssertSequenceEqual(new { Item = 123, IsFirst = true, IsLast = true });
}

[Fact]
public void TagFirstLastWithSourceSequenceOfTwo()
{
using var sequence = TestingSequence.Of(123, 456);

var result = sequence.TagFirstLast((item, isFirst, isLast) => new { Item = item, IsFirst = isFirst, IsLast = isLast });
result.AssertSequenceEqual(
new { Item = 123, IsFirst = true, IsLast = false },
new { Item = 456, IsFirst = false, IsLast = true });
using (seq)
{
var result = seq.TagFirstLast();
result.AssertSequenceEqual(
Enumerable.Range(0, n)
.Select(x => (x, x == 0, x == n - 1)));
}
}

[Fact]
public void TagFirstLastWithSourceSequenceOfThree()
public void TagFirstLastListBehavior()
{
using var sequence = TestingSequence.Of(123, 456, 789);
using var seq = Enumerable.Range(0, 10_000).AsBreakingList();

var result = sequence.TagFirstLast((item, isFirst, isLast) => new { Item = item, IsFirst = isFirst, IsLast = isLast });
result.AssertSequenceEqual(
new { Item = 123, IsFirst = true, IsLast = false },
new { Item = 456, IsFirst = false, IsLast = false },
new { Item = 789, IsFirst = false, IsLast = true });
var result = seq.TagFirstLast();
Assert.Equal(10_000, result.Count());
Assert.Equal((0, true, false), result.ElementAt(0));
Assert.Equal((30, false, false), result.ElementAt(30));
Assert.Equal((9_999, false, true), result.ElementAt(^1));
}
}