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[ElementAt] add extension.
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‎Documents/BenchmarksResults/ElementAtOnArray.md‎

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## ElementAtOnArray
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### Source
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[ElementAtOnArray.cs](../../src/StructLinq.Benchmark/ElementAtOnArray.cs)
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### Results:
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``` ini
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BenchmarkDotNet=v0.12.0, OS=Windows 10.0.19041
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Intel Core i7-7700 CPU 3.60GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
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.NET Core SDK=3.1.403
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[Host] : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
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DefaultJob : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
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```
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| Method | Mean | Error | StdDev | Ratio | Gen 0 | Gen 1 | Gen 2 | Allocated |
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|-------------------- |----------:|----------:|----------:|------:|-------:|------:|------:|----------:|
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| Linq | 26.625 ns | 0.2574 ns | 0.2408 ns | 1.00 | - | - | - | - |
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| EnumerableLinq | 26.390 ns | 0.4745 ns | 0.3962 ns | 0.99 | - | - | - | - |
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| StructLinq | 13.418 ns | 0.2688 ns | 0.2761 ns | 0.51 | 0.0076 | - | - | 32 B |
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| StructLinqZeroAlloc | 4.414 ns | 0.0438 ns | 0.0366 ns | 0.17 | - | - | - | - |

‎README.md‎

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@@ -181,7 +181,10 @@ Following extensions are available for :
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- `Intersect`([zero allocation](Documents/BenchmarksResults/Intersect.md))
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- `First`
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- `FirstOrDefault`
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- `Last`
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- `LastOrDefault`
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- `ElementAt`
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- `ElementAtOrDefault`
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‎src/StructLinq.Benchmark/ElementAtOnArray.cs‎

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using System.Collections.Generic;
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using System.Linq;
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using BenchmarkDotNet.Attributes;
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namespace StructLinq.Benchmark
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{
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[MemoryDiagnoser]
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public class ElementAtOnArray
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{
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private const int Count = 1000;
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private readonly int[] array;
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private readonly IEnumerable<int> enumerable;
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public ElementAtOnArray()
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{
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array = Enumerable.ToArray(Enumerable.Range(0, Count));
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enumerable = Enumerable.ToArray(Enumerable.Range(0, Count));
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}
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[Benchmark(Baseline = true)]
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public int Linq() => array.ElementAt(Count / 2);
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[Benchmark]
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public int EnumerableLinq() => enumerable.ElementAt(Count / 2);
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[Benchmark]
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public int StructLinq() => array.ToStructEnumerable().ElementAt(Count / 2);
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[Benchmark]
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public int StructLinqZeroAlloc() => array.ToStructEnumerable().ElementAt(Count / 2, x=>x);
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}
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}

‎src/StructLinq.Tests/ElementAtOnCollectionTests.cs‎

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using System;
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using System.Linq;
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using Xunit;
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namespace StructLinq.Tests
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{
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public class ElementAtOnCollectionTests
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{
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[Fact]
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public void ShouldReturnElementAtElement()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAt(i));
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}
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}
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[Fact]
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public void ShouldReturnElementAtElementZeroAlloc()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAt(i, x=>x));
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}
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldThrowException(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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Assert.Throws<ArgumentOutOfRangeException>(() => enumerable.ElementAt(index));
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldThrowExceptionZeroAlloc(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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Assert.Throws<ArgumentOutOfRangeException>(() => enumerable.ElementAt(index, x=>x));
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}
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}
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}

‎src/StructLinq.Tests/ElementAtOrDefaultOnCollectionTests.cs‎

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using System.Linq;
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using Xunit;
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namespace StructLinq.Tests
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{
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public class ElementAtOrDefaultOnCollectionTests
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{
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[Fact]
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public void ShouldReturnElementAtElement()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAtOrDefault(i));
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}
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}
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[Fact]
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public void ShouldReturnElementAtElementZeroAlloc()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAtOrDefault(i, x=>x));
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}
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldReturnDefault(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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Assert.Equal(default, enumerable.ElementAtOrDefault(index));
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldReturnDefaultZeroAlloc(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable();
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Assert.Equal(default, enumerable.ElementAtOrDefault(index, x=>x));
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}
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}
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}

‎src/StructLinq.Tests/ElementAtOrDefaultTests.cs‎

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using System.Linq;
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using Xunit;
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namespace StructLinq.Tests
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{
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public class ElementAtOrDefaultTests
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{
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[Fact]
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public void ShouldReturnElementAtElement()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAtOrDefault(i));
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}
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}
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[Fact]
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public void ShouldReturnElementAtElementZeroAlloc()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAtOrDefault(i, x=>x));
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}
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldReturnDefault(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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Assert.Equal(default, enumerable.ElementAtOrDefault(index));
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldReturnDefaultZeroAlloc(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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Assert.Equal(default, enumerable.ElementAtOrDefault(index, x=>x));
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}
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}
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}

‎src/StructLinq.Tests/ElementAtTests.cs‎

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using System;
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using System.Linq;
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using Xunit;
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namespace StructLinq.Tests
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{
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public class ElementAtTests
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{
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[Fact]
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public void ShouldReturnElementAtElement()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAt(i));
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}
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}
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[Fact]
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public void ShouldReturnElementAtElementZeroAlloc()
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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var array = enumerable.ToArray();
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for (int i = 0; i < array.Length; i++)
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{
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Assert.Equal(array[i], enumerable.ElementAt(i, x=>x));
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}
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldThrowException(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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Assert.Throws<ArgumentOutOfRangeException>(() => enumerable.ElementAt(index));
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}
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[Theory]
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[InlineData(-10)]
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[InlineData(-1)]
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[InlineData(10)]
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[InlineData(20)]
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public void ShouldThrowExceptionZeroAlloc(int index)
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{
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var enumerable = Enumerable.Range(-1, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x => true);
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Assert.Throws<ArgumentOutOfRangeException>(() => enumerable.ElementAt(index, x=>x));
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}
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}
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}

‎src/StructLinq.Tests/FirstTests.cs‎

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var array = Enumerable.Range(0, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x=> true)
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.First()
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.Should()
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.Be(0);
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var array = Enumerable.Range(0, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x=> true, x=> x)
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.First(x=>x)
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.Should()
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.Be(0);
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var array = Enumerable.Range(0, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x=> true)
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.First(x=> x > 5)
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.Should()
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.Be(6);
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var array = Enumerable.Range(0, 10)
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.ToArray()
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.ToStructEnumerable()
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.Where(x=> true, x=>x)
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.First(x=> x > 5, x=> x)
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.Should()
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.Be(6);

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