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50 lines
2.2 KiB
C#
50 lines
2.2 KiB
C#
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// See the LICENCE file in the repository root for full licence text.
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using System;
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using System.Collections.Generic;
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namespace osu.Game.Utils
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{
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/// <summary>
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/// This string comparer is something of a cross-over between <see cref="StringComparer.Ordinal"/> and <see cref="StringComparer.OrdinalIgnoreCase"/>.
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/// <see cref="StringComparer.OrdinalIgnoreCase"/> is used first, but <see cref="StringComparer.Ordinal"/> is used as a tie-breaker.
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/// </summary>
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/// <remarks>
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/// This comparer's behaviour somewhat emulates <see cref="StringComparer.InvariantCulture"/>,
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/// but non-ordinal comparers - both culture-aware and culture-invariant - have huge performance overheads due to i18n factors (up to 5x slower).
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/// </remarks>
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/// <example>
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/// Given the following strings to sort: <c>[A, B, C, D, a, b, c, d, A]</c> and a stable sorting algorithm:
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/// <list type="bullet">
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/// <item>
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/// <see cref="StringComparer.Ordinal"/> would return <c>[A, A, B, C, D, a, b, c, d]</c>.
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/// This is undesirable as letters are interleaved.
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/// </item>
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/// <item>
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/// <see cref="StringComparer.OrdinalIgnoreCase"/> would return <c>[A, a, A, B, b, C, c, D, d]</c>.
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/// Different letters are not interleaved, but because case is ignored, the As are left in arbitrary order.
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/// </item>
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/// </list>
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/// <item>
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/// <see cref="OrdinalSortByCaseStringComparer"/> would return <c>[a, A, A, b, B, c, C, d, D]</c>, which is the expected behaviour.
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/// </item>
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/// </example>
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public class OrdinalSortByCaseStringComparer : IComparer<string>
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{
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public static readonly OrdinalSortByCaseStringComparer DEFAULT = new OrdinalSortByCaseStringComparer();
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private OrdinalSortByCaseStringComparer()
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{
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}
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public int Compare(string? a, string? b)
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{
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int result = StringComparer.OrdinalIgnoreCase.Compare(a, b);
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if (result == 0)
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result = -StringComparer.Ordinal.Compare(a, b); // negative to place lowercase letters before uppercase.
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return result;
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}
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}
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}
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