src/Lucene.Net.Queries/Function/ValueSources/LiteralValueSource.cs

// Lucene version compatibility level 4.8.1
using Lucene.Net.Index;
using Lucene.Net.Queries.Function.DocValues;
using Lucene.Net.Util;
using System;
using System.Collections;

namespace Lucene.Net.Queries.Function.ValueSources
{
    /*
     * Licensed to the Apache Software Foundation (ASF) under one or more
     * contributor license agreements.  See the NOTICE file distributed with
     * this work for additional information regarding copyright ownership.
     * The ASF licenses this file to You under the Apache License, Version 2.0
     * (the "License"); you may not use this file except in compliance with
     * the License.  You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    /// <summary>
    /// Pass a the field value through as a <see cref="string"/>, no matter the type // Q: doesn't this mean it's a "str"?
    /// </summary>
    public class LiteralValueSource : ValueSource
    {
        protected readonly string m_str;
        protected readonly BytesRef m_bytesRef;

        public LiteralValueSource(string str)
        {
            this.m_str = str;
            this.m_bytesRef = new BytesRef(str);
        }

        /// <summary>
        /// returns the literal value </summary>
        public virtual string Value => m_str;

        public override FunctionValues GetValues(IDictionary context, AtomicReaderContext readerContext)
        {

            return new StrDocValuesAnonymousClass(this, this);
        }

        private class StrDocValuesAnonymousClass : StrDocValues
        {
            private readonly LiteralValueSource outerInstance;

            public StrDocValuesAnonymousClass(LiteralValueSource outerInstance, LiteralValueSource @this)
                : base(@this)
            {
                this.outerInstance = outerInstance;
            }

            public override string StrVal(int doc)
            {
                return outerInstance.m_str;
            }

            public override bool BytesVal(int doc, BytesRef target)
            {
                target.CopyBytes(outerInstance.m_bytesRef);
                return true;
            }

            public override string ToString(int doc)
            {
                return outerInstance.m_str;
            }
        }

        public override string GetDescription()
        {
            return "literal(" + m_str + ")";
        }

        public override bool Equals(object o)
        {
            if (this == o)
            {
                return true;
            }
            if (!(o is LiteralValueSource that))
                return false;
            return m_str.Equals(that.m_str, StringComparison.Ordinal);

        }

        public static readonly int hash = typeof(LiteralValueSource).GetHashCode();
        public override int GetHashCode()
        {
            return hash + m_str.GetHashCode();
        }
    }
}