134 lines
6.2 KiB
C#
134 lines
6.2 KiB
C#
// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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using System;
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using System.Runtime.CompilerServices;
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#if NETSTANDARD
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using System.Runtime.InteropServices;
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#endif
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using CommunityToolkit.HighPerformance.Enumerables;
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using CommunityToolkit.HighPerformance.Helpers.Internals;
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namespace CommunityToolkit.HighPerformance;
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/// <summary>
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/// Helpers for working with the <see cref="string"/> type.
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/// </summary>
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public static class StringExtensions
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{
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/// <summary>
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/// Returns a reference to the first element within a given <see cref="string"/>, with no bounds checks.
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/// </summary>
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/// <param name="text">The input <see cref="string"/> instance.</param>
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/// <returns>A reference to the first element within <paramref name="text"/>, or the location it would have used, if <paramref name="text"/> is empty.</returns>
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/// <remarks>This method doesn't do any bounds checks, therefore it is responsibility of the caller to perform checks in case the returned value is dereferenced.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static ref char DangerousGetReference(this string text)
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{
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#if NETCOREAPP3_1_OR_GREATER
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return ref Unsafe.AsRef(text.GetPinnableReference());
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#else
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return ref MemoryMarshal.GetReference(text.AsSpan());
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#endif
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}
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/// <summary>
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/// Returns a reference to an element at a specified index within a given <see cref="string"/>, with no bounds checks.
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/// </summary>
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/// <param name="text">The input <see cref="string"/> instance.</param>
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/// <param name="i">The index of the element to retrieve within <paramref name="text"/>.</param>
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/// <returns>A reference to the element within <paramref name="text"/> at the index specified by <paramref name="i"/>.</returns>
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/// <remarks>This method doesn't do any bounds checks, therefore it is responsibility of the caller to ensure the <paramref name="i"/> parameter is valid.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static ref char DangerousGetReferenceAt(this string text, int i)
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{
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#if NETCOREAPP3_1_OR_GREATER
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ref char r0 = ref Unsafe.AsRef(text.GetPinnableReference());
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#else
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ref char r0 = ref MemoryMarshal.GetReference(text.AsSpan());
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#endif
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ref char ri = ref Unsafe.Add(ref r0, (nint)(uint)i);
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return ref ri;
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}
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/// <summary>
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/// Counts the number of occurrences of a given character into a target <see cref="string"/> instance.
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/// </summary>
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/// <param name="text">The input <see cref="string"/> instance to read.</param>
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/// <param name="c">The character to look for.</param>
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/// <returns>The number of occurrences of <paramref name="c"/> in <paramref name="text"/>.</returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static int Count(this string text, char c)
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{
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ref char r0 = ref text.DangerousGetReference();
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nint length = (nint)(uint)text.Length;
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return (int)SpanHelper.Count(ref r0, length, c);
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}
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/// <summary>
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/// Enumerates the items in the input <see cref="string"/> instance, as pairs of value/index values.
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/// This extension should be used directly within a <see langword="foreach"/> loop:
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/// <code>
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/// string text = "Hello, world!";
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///
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/// foreach (var item in text.Enumerate())
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/// {
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/// // Access the index and value of each item here...
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/// int index = item.Index;
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/// char value = item.Value;
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/// }
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/// </code>
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/// The compiler will take care of properly setting up the <see langword="foreach"/> loop with the type returned from this method.
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/// </summary>
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/// <param name="text">The source <see cref="string"/> to enumerate.</param>
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/// <returns>A wrapper type that will handle the value/index enumeration for <paramref name="text"/>.</returns>
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/// <remarks>The returned <see cref="ReadOnlySpanEnumerable{T}"/> value shouldn't be used directly: use this extension in a <see langword="foreach"/> loop.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static ReadOnlySpanEnumerable<char> Enumerate(this string text)
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{
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return new(text.AsSpan());
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}
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/// <summary>
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/// Tokenizes the values in the input <see cref="string"/> instance using a specified separator.
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/// This extension should be used directly within a <see langword="foreach"/> loop:
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/// <code>
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/// string text = "Hello, world!";
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///
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/// foreach (var token in text.Tokenize(','))
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/// {
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/// // Access the tokens here...
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/// }
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/// </code>
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/// The compiler will take care of properly setting up the <see langword="foreach"/> loop with the type returned from this method.
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/// </summary>
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/// <param name="text">The source <see cref="string"/> to tokenize.</param>
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/// <param name="separator">The separator character to use.</param>
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/// <returns>A wrapper type that will handle the tokenization for <paramref name="text"/>.</returns>
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/// <remarks>The returned <see cref="ReadOnlySpanTokenizer{T}"/> value shouldn't be used directly: use this extension in a <see langword="foreach"/> loop.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static ReadOnlySpanTokenizer<char> Tokenize(this string text, char separator)
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{
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return new(text.AsSpan(), separator);
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}
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/// <summary>
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/// Gets a content hash from the input <see cref="string"/> instance using the Djb2 algorithm.
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/// For more info, see the documentation for <see cref="ReadOnlySpanExtensions.GetDjb2HashCode{T}"/>.
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/// </summary>
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/// <param name="text">The source <see cref="string"/> to enumerate.</param>
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/// <returns>The Djb2 value for the input <see cref="string"/> instance.</returns>
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/// <remarks>The Djb2 hash is fully deterministic and with no random components.</remarks>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static unsafe int GetDjb2HashCode(this string text)
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{
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ref char r0 = ref text.DangerousGetReference();
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nint length = (nint)(uint)text.Length;
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return SpanHelper.GetDjb2HashCode(ref r0, length);
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}
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}
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