Utilities.cs

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using System.Collections.Generic;
 
namespace System.Linq;
 
internal static class Utilities
{
    public static bool AreEqualityComparersEqual<TSource>(IEqualityComparer<TSource> left, IEqualityComparer<TSource> right)
    {
        if (left == right)
        {
            return true;
        }
        EqualityComparer<TSource> @default = EqualityComparer<TSource>.Default;
        if (left == null)
        {
            if (right != @default)
            {
                return right.Equals(@default);
            }
            return true;
        }
        if (right == null)
        {
            if (left != @default)
            {
                return left.Equals(@default);
            }
            return true;
        }
        return left.Equals(right);
    }
 
    public static Func<TSource, bool> CombinePredicates<TSource>(Func<TSource, bool> predicate1, Func<TSource, bool> predicate2)
    {
        return (TSource x) => predicate1(x) && predicate2(x);
    }
 
    public static Func<TSource, TResult> CombineSelectors<TSource, TMiddle, TResult>(Func<TSource, TMiddle> selector1, Func<TMiddle, TResult> selector2)
    {
        return (TSource x) => selector2(selector1(x));
    }
}