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Simplify ZipLongest implementation #905

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Simplify ZipLongest implementation #905

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65 changes: 59 additions & 6 deletions MoreLinq/ZipLongest.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 @@ -56,13 +57,13 @@ static partial class MoreEnumerable
public static IEnumerable<TResult> ZipLongest<TFirst, TSecond, TResult>(
this IEnumerable<TFirst> first,
IEnumerable<TSecond> second,
Func<TFirst, TSecond, TResult> resultSelector)
Func<TFirst?, TSecond?, TResult> resultSelector)
{
if (first == null) throw new ArgumentNullException(nameof(first));
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), 1);
return ZipLongestImpl(first, second, Enumerable.Repeat(default(object?), int.MaxValue), Enumerable.Repeat(default(object?), int.MaxValue), (a, b, _, _) => resultSelector(a, b), 2);
}

/// <summary>
Expand Down Expand Up @@ -103,14 +104,14 @@ public static IEnumerable<TResult> ZipLongest<T1, T2, T3, TResult>(
this IEnumerable<T1> first,
IEnumerable<T2> second,
IEnumerable<T3> third,
Func<T1, T2, T3, TResult> resultSelector)
Func<T1?, T2?, T3?, TResult> resultSelector)
{
if (first == null) throw new ArgumentNullException(nameof(first));
if (second == null) throw new ArgumentNullException(nameof(second));
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), 2);
return ZipLongestImpl(first, second, third, Enumerable.Repeat(default(object?), int.MaxValue), (a, b, c, _) => resultSelector(a, b, c), 3);
}

/// <summary>
Expand Down Expand Up @@ -155,15 +156,67 @@ public static IEnumerable<TResult> ZipLongest<T1, T2, T3, T4, TResult>(
IEnumerable<T2> second,
IEnumerable<T3> third,
IEnumerable<T4> fourth,
Func<T1, T2, T3, T4, TResult> resultSelector)
Func<T1?, T2?, T3?, T4?, TResult> resultSelector)
{
if (first == null) throw new ArgumentNullException(nameof(first));
if (second == null) throw new ArgumentNullException(nameof(second));
if (third == null) throw new ArgumentNullException(nameof(third));
if (fourth == null) throw new ArgumentNullException(nameof(fourth));
if (resultSelector == null) throw new ArgumentNullException(nameof(resultSelector));

return ZipImpl(first, second, third, fourth, resultSelector, 3);
return ZipLongestImpl(first, second, third, fourth, resultSelector, 4);
}

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

while (true)
{
var terms = 4;

var v1 = default(T1?);
if (e1.MoveNext())
{
v1 = e1.Current;
terms--;
}

var v2 = default(T2?);
if (e2.MoveNext())
{
v2 = e2.Current;
terms--;
}

var v3 = default(T3?);
if (e3.MoveNext())
{
v3 = e3.Current;
terms--;
}

var v4 = default(T4?);
if (e4.MoveNext())
{
v4 = e4.Current;
terms--;
}

if (terms >= limit)
yield break;

yield return resultSelector(v1, v2, v3, v4);
}
}
}
}