Example.cs

using System;
using System.Collections.Generic;

namespace M
{
    public sealed class MemoizerBuilder<T1, T2, T3, T4, TOut>
    {
        private readonly Func<T1, T2, T3, T4, TOut> func;

        private IEqualityComparer<T1> equalityComparer1;

        private IEqualityComparer<T2> equalityComparer2;

        private IEqualityComparer<T3> equalityComparer3;

        private IEqualityComparer<T4> equalityComparer4;

        public MemoizerBuilder(Func<T1, T2, T3, T4, TOut> func) => this.func = func ?? throw new ArgumentNullException(nameof(func));

        public MemoizerBuilder<T1, T2, T3, T4, TOut> WithEqualityComparer1(IEqualityComparer<T1> equalityComparer1)
        {
            this.equalityComparer1 = equalityComparer1;
            return this;
        }

        public MemoizerBuilder<T1, T2, T3, T4, TOut> WithEqualityComparer2(IEqualityComparer<T2> equalityComparer2)
        {
            this.equalityComparer2 = equalityComparer2;
            return this;
        }

        public MemoizerBuilder<T1, T2, T3, T4, TOut> WithEqualityComparer3(IEqualityComparer<T3> equalityComparer3)
        {
            this.equalityComparer3 = equalityComparer3;
            return this;
        }

        public MemoizerBuilder<T1, T2, T3, T4, TOut> WithEqualityComparer4(IEqualityComparer<T4> equalityComparer4)
        {
            this.equalityComparer4 = equalityComparer4;
            return this;
        }

        public Func<T1, T2, T3, T4, TOut> Build()
        {
            var ec1 = this.equalityComparer1 ?? EqualityComparer<T1>.Default;
            var ec2 = this.equalityComparer2 ?? EqualityComparer<T2>.Default;
            var ec3 = this.equalityComparer3 ?? EqualityComparer<T3>.Default;
            var ec4 = this.equalityComparer4 ?? EqualityComparer<T4>.Default;
            bool hasValue = false;
            (T1 v1, T2 v2, T3 v3, T4 v4, TOut vResult) lastCall = default;
            return MyMemoized;
            TOut MyMemoized(T1 v1, T2 v2, T3 v3, T4 v4)
            {
                if (!(hasValue &&
                      ec1.Equals(v1, lastCall.v1) &&
                      ec2.Equals(v2, lastCall.v2) &&
                      ec3.Equals(v3, lastCall.v3) &&
                      ec4.Equals(v4, lastCall.v4)))
                {
                    hasValue = true;
                    lastCall = (v1, v2, v3, v4, this.func(v1, v2, v3, v4));
                }

                return lastCall.vResult;
            }
        }
    }
}