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Simplify ZipShortest implementation #904

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Simplify ZipShortest implementation #904

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13 changes: 13 additions & 0 deletions MoreLinq.Test/ZipShortestTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,19 @@ public void ZipShortestIsLazy()
bs.ZipShortest(bs, BreakingFunc.Of<int, int, int>());
}

[Test]
[TestCase(1), TestCase(2), TestCase(3), TestCase(4)]
public void ZipShortestEndsAtShortestSequence(int shortSequence)
{
var seq1 = Enumerable.Range(1, shortSequence == 1 ? 2 : 3);
var seq2 = Enumerable.Range(1, shortSequence == 2 ? 2 : 3);
var seq3 = Enumerable.Range(1, shortSequence == 3 ? 2 : 3);
var seq4 = Enumerable.Range(1, shortSequence == 4 ? 2 : 3);

var seq = seq1.ZipShortest(seq2, seq3, seq4, (a, _, _, _) => a);
seq.AssertSequenceEqual(1, 2);
}

[Test]
public void MoveNextIsNotCalledUnnecessarilyWhenFirstIsShorter()
{
Expand Down
40 changes: 31 additions & 9 deletions MoreLinq/ZipShortest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ namespace MoreLinq
{
using System;
using System.Collections.Generic;
using System.Linq;

static partial class MoreEnumerable
{
Expand Down Expand Up @@ -64,7 +65,7 @@ public static IEnumerable<TResult> ZipShortest<TFirst, TSecond, TResult>(
if (second == null) throw new ArgumentNullException(nameof(second));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

return ZipImpl<TFirst, TSecond, object, object, TResult>(first, second, null, null, (a, b, _, _) => resultSelector(a, b));
return ZipShortestImpl(first, second, Enumerable.Repeat(default(object?), int.MaxValue), Enumerable.Repeat(default(object?), int.MaxValue), (a, b, _, _) => resultSelector(a, b));
}

/// <summary>
Expand Down Expand Up @@ -115,7 +116,7 @@ public static IEnumerable<TResult> ZipShortest<T1, T2, T3, TResult>(
if (third == null) throw new ArgumentNullException(nameof(third));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

return ZipImpl<T1, T2, T3, object, TResult>(first, second, third, null, (a, b, c, _) => resultSelector(a, b, c));
return ZipShortestImpl(first, second, third, Enumerable.Repeat(default(object?), int.MaxValue), (a, b, c, _) => resultSelector(a, b, c));
}

/// <summary>
Expand Down Expand Up @@ -171,17 +172,38 @@ public static IEnumerable<TResult> ZipShortest<T1, T2, T3, T4, TResult>(
if (fourth == null) throw new ArgumentNullException(nameof(fourth));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

return ZipImpl(first, second, third, fourth, resultSelector);
return ZipShortestImpl(first, second, third, fourth, resultSelector);
}

static IEnumerable<TResult> ZipImpl<T1, T2, T3, T4, TResult>(
IEnumerable<T1> s1,
IEnumerable<T2> s2,
IEnumerable<T3>? s3,
IEnumerable<T4>? s4,
private static IEnumerable<TResult> ZipShortestImpl<T1, T2, T3, T4, TResult>(
IEnumerable<T1> s1,
IEnumerable<T2> s2,
IEnumerable<T3> s3,
IEnumerable<T4> s4,
Func<T1, T2, T3, T4, TResult> resultSelector)
{
return ZipImpl(s1, s2, s3, s4, resultSelector, 0);
using var e1 = s1.GetEnumerator();
using var e2 = s2.GetEnumerator();
using var e3 = s3.GetEnumerator();
using var e4 = s4.GetEnumerator();

while (true)
{
if (!e1.MoveNext())
yield break;
if (!e2.MoveNext())
yield break;
if (!e3.MoveNext())
yield break;
if (!e4.MoveNext())
yield break;

yield return resultSelector(
e1.Current,
e2.Current,
e3.Current,
e4.Current);
}
}
}
}