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197 lines
7.6 KiB
197 lines
7.6 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 PrependEnumerator GetEnumerator() => new PrependEnumerator(this);
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public struct PrependEnumerator : IEnumerator<T>
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{
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private readonly IEnumerator<T> restEnum;
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private readonly PrependEnumerable<T> enumerable;
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private int state;
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internal PrependEnumerator(PrependEnumerable<T> enumerable)
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{
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this.enumerable = enumerable;
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restEnum = enumerable.rest.GetEnumerator();
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state = 0;
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Current = default;
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}
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public T Current { get; private set; }
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object IEnumerator.Current => Current;
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public void Dispose() => restEnum.Dispose();
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public bool MoveNext()
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{
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switch (state)
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{
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case 0:
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Current = enumerable.first;
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state++;
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return true;
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case 1:
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if (!restEnum.MoveNext())
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{
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state = 2;
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return false;
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}
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else
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Current = restEnum.Current;
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return true;
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case 2:
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default:
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return false;
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}
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}
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public void Reset()
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{
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restEnum.Reset();
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state = 0;
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}
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}
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IEnumerator<T> IEnumerable<T>.GetEnumerator() => new PrependEnumerator(this);
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IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
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}
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/// <summary>
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/// Adds a value to the end 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="app">the value to append to <paramref name="seq"/></param>
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/// <returns>a new sequence ending with <paramref name="app"/></returns>
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public static IEnumerable<T> Append<T>(this IEnumerable<T> seq, T app)
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=> new AppendEnumerable<T>(seq, app);
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private sealed class AppendEnumerable<T> : IEnumerable<T>
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{
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private readonly IEnumerable<T> rest;
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private readonly T last;
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public AppendEnumerable(IEnumerable<T> rest, T last)
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{
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this.rest = rest;
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this.last = last;
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}
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public AppendEnumerator GetEnumerator() => new AppendEnumerator(this);
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public struct AppendEnumerator : IEnumerator<T>
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{
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private readonly IEnumerator<T> restEnum;
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private readonly AppendEnumerable<T> enumerable;
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private int state;
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internal AppendEnumerator(AppendEnumerable<T> enumerable)
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{
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this.enumerable = enumerable;
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restEnum = enumerable.rest.GetEnumerator();
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state = 0;
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Current = default;
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}
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public T Current { get; private set; }
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object IEnumerator.Current => Current;
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public void Dispose() => restEnum.Dispose();
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public bool MoveNext()
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{
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switch (state)
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{
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case 0:
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if (!restEnum.MoveNext())
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{
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state = 1;
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goto case 1;
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}
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else
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Current = restEnum.Current;
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return true;
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case 1:
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Current = enumerable.last;
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state++;
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return true;
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case 2:
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default:
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return false;
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}
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}
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public void Reset()
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{
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restEnum.Reset();
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state = 0;
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}
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}
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IEnumerator<T> IEnumerable<T>.GetEnumerator() => GetEnumerator();
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IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
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}
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/// <summary>
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/// LINQ extension method that filters <see langword="null"/> elements out of an enumeration.
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/// </summary>
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/// <typeparam name="T">the type of the enumeration</typeparam>
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/// <param name="self">the enumeration to filter</param>
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/// <returns>a filtered enumerable</returns>
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public static IEnumerable<T> NonNull<T>(this IEnumerable<T> self) where T : class
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=> self.Where(o => o != null);
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/// <summary>
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/// LINQ extension method that filters <see langword="null"/> elements out of an enumeration based on a converter.
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/// </summary>
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/// <typeparam name="T">the type of the enumeration</typeparam>
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/// <typeparam name="U">the type to compare to null</typeparam>
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/// <param name="self">the enumeration to filter</param>
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/// <param name="pred">the predicate to select for filtering</param>
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/// <returns>a filtered enumerable</returns>
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public static IEnumerable<T> NonNull<T, U>(this IEnumerable<T> self, Func<T, U> pred) where U : class
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=> self.Where(o => pred(o) != null);
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/// <summary>
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/// LINQ extension method that filters <see langword="null"/> elements from an enumeration of nullable types.
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/// </summary>
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/// <typeparam name="T">the underlying type of the nullable enumeration</typeparam>
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/// <param name="self">the enumeration to filter</param>
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/// <returns>a filtered enumerable</returns>
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public static IEnumerable<T> NonNull<T>(this IEnumerable<T?> self) where T : struct
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=> self.Where(o => o != null).Select(o => o.Value);
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}
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}
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