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45 lines
1.5 KiB
45 lines
1.5 KiB
using System;
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using System.Collections;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading.Tasks;
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namespace IPA.Utilities
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{
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/// <summary>
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/// Extensions for <see cref="IEnumerable{T}"/> that don't currently exist in <c>System.Linq</c>.
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/// </summary>
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public static class EnumerableExtensions
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{
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/// <summary>
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/// Adds a value to the beginning of the sequence.
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/// </summary>
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/// <typeparam name="T">the type of the elements of <paramref name="seq"/></typeparam>
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/// <param name="seq">a sequence of values</param>
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/// <param name="prep">the value to prepend to <paramref name="seq"/></param>
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/// <returns>a new sequence beginning with <paramref name="prep"/></returns>
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public static IEnumerable<T> Prepend<T>(this IEnumerable<T> seq, T prep)
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=> new PrependEnumerable<T>(seq, prep);
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private sealed class PrependEnumerable<T> : IEnumerable<T>
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{
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private readonly IEnumerable<T> rest;
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private readonly T first;
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public PrependEnumerable(IEnumerable<T> rest, T first)
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{
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this.rest = rest;
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this.first = first;
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}
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public IEnumerator<T> GetEnumerator()
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{
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yield return first;
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foreach (var v in rest) yield return v;
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}
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IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
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}
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}
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}
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