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.NET-Community-Toolkit/CommunityToolkit.HighPerformance/Enumerables/ReadOnlySpanEnumerable{T}.cs

155 lines
5.0 KiB
C#

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
namespace CommunityToolkit.HighPerformance.Enumerables;
/// <summary>
/// A <see langword="ref"/> <see langword="struct"/> that enumerates the items in a given <see cref="ReadOnlySpan{T}"/> instance.
/// </summary>
/// <typeparam name="T">The type of items to enumerate.</typeparam>
[EditorBrowsable(EditorBrowsableState.Never)]
public ref struct ReadOnlySpanEnumerable<T>
{
/// <summary>
/// The source <see cref="ReadOnlySpan{T}"/> instance.
/// </summary>
private readonly ReadOnlySpan<T> span;
/// <summary>
/// The current index within <see cref="span"/>.
/// </summary>
private int index;
/// <summary>
/// Initializes a new instance of the <see cref="ReadOnlySpanEnumerable{T}"/> struct.
/// </summary>
/// <param name="span">The source <see cref="ReadOnlySpan{T}"/> instance.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpanEnumerable(ReadOnlySpan<T> span)
{
this.span = span;
this.index = -1;
}
/// <summary>
/// Implements the duck-typed <see cref="IEnumerable{T}.GetEnumerator"/> method.
/// </summary>
/// <returns>An <see cref="ReadOnlySpanEnumerable{T}"/> instance targeting the current <see cref="ReadOnlySpan{T}"/> value.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public readonly ReadOnlySpanEnumerable<T> GetEnumerator() => this;
/// <summary>
/// Implements the duck-typed <see cref="System.Collections.IEnumerator.MoveNext"/> method.
/// </summary>
/// <returns><see langword="true"/> whether a new element is available, <see langword="false"/> otherwise</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public bool MoveNext()
{
return ++this.index < this.span.Length;
}
/// <summary>
/// Gets the duck-typed <see cref="IEnumerator{T}.Current"/> property.
/// </summary>
public readonly Item Current
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
#if NETSTANDARD2_1_OR_GREATER
ref T r0 = ref MemoryMarshal.GetReference(this.span);
ref T ri = ref Unsafe.Add(ref r0, (nint)(uint)this.index);
// See comment in SpanEnumerable<T> about this
return new(ref ri, this.index);
#else
return new(this.span, this.index);
#endif
}
}
/// <summary>
/// An item from a source <see cref="Span{T}"/> instance.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public readonly ref struct Item
{
/// <summary>
/// The source <see cref="ReadOnlySpan{T}"/> instance.
/// </summary>
private readonly ReadOnlySpan<T> span;
#if NETSTANDARD2_1_OR_GREATER
/// <summary>
/// Initializes a new instance of the <see cref="Item"/> struct.
/// </summary>
/// <param name="value">A reference to the target value.</param>
/// <param name="index">The index of the target value.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Item(ref T value, int index)
{
this.span = MemoryMarshal.CreateReadOnlySpan(ref value, index);
}
#else
/// <summary>
/// The current index within <see cref="span"/>.
/// </summary>
private readonly int index;
/// <summary>
/// Initializes a new instance of the <see cref="Item"/> struct.
/// </summary>
/// <param name="span">The source <see cref="ReadOnlySpan{T}"/> instance.</param>
/// <param name="index">The current index within <paramref name="span"/>.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Item(ReadOnlySpan<T> span, int index)
{
this.span = span;
this.index = index;
}
#endif
/// <summary>
/// Gets the reference to the current value.
/// </summary>
public ref readonly T Value
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
#if NETSTANDARD2_1_OR_GREATER
return ref MemoryMarshal.GetReference(this.span);
#else
ref T r0 = ref MemoryMarshal.GetReference(this.span);
ref T ri = ref Unsafe.Add(ref r0, (nint)(uint)this.index);
return ref ri;
#endif
}
}
/// <summary>
/// Gets the current index.
/// </summary>
public int Index
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
#if NETSTANDARD2_1_OR_GREATER
return this.span.Length;
#else
return this.index;
#endif
}
}
}
}