| // 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. |
| |
| using System; |
| using Org.Apache.REEF.Utilities.Logging; |
| |
| namespace Org.Apache.REEF.Utilities |
| { |
| /// <summary> |
| /// A convenience class that indicates whether a variable is set or not. |
| /// The generic type T can either be of nullable or non-nullable type. |
| /// </summary> |
| [Serializable] |
| public sealed class Optional<T> |
| { |
| private readonly bool _isSet = false; |
| private readonly T _value; |
| |
| private Optional(T value) |
| { |
| _isSet = true; |
| _value = value; |
| } |
| |
| private Optional() |
| { |
| _value = default(T); |
| } |
| |
| /// <summary> |
| /// Gets the Value associated with the <see cref="Optional{T}"/> object. |
| /// If empty and <see cref="T"/> is nullable, the Value will return null. |
| /// If empty and <see cref="T"/> is non-nullable, the Value will return default(T). |
| /// </summary> |
| public T Value |
| { |
| get { return _value; } |
| } |
| |
| /// <summary> |
| /// Creates an <see cref="Optional{T}"/> with <see cref="Value"/> of parameter <see cref="value"/>. |
| /// If <see cref="T"/> is nullable and null is passed in, an <see cref="ArgumentNullException"/> will be thrown. |
| /// If <see cref="T"/> is non-nullable and default(T) is passed in, a non-empty <see cref="Optional{T}"/> object will be returned. |
| /// </summary> |
| public static Optional<T> Of(T value) |
| { |
| if (value == null) |
| { |
| Diagnostics.Exceptions.Throw(new ArgumentNullException("value", "Passed a null value. Use OfNullable() instead"), Logger.GetLogger(typeof(Optional<T>))); |
| } |
| return new Optional<T>(value); |
| } |
| |
| /// <summary> |
| /// Creates an empty <see cref="Optional{T}"/>. |
| /// </summary> |
| public static Optional<T> Empty() |
| { |
| return new Optional<T>(); |
| } |
| |
| /// <summary> |
| /// Creates an <see cref="Optional{T}"/> with <see cref="Value"/> of parameter <see cref="value"/>. |
| /// If <see cref="T"/> is nullable and null is passed in, an empty <see cref="Optional{T}"/> will be returned. |
| /// If <see cref="T"/> is non-nullable and default(T) is passed in, a non-empty <see cref="Optional{T}"/> object will be returned. |
| /// </summary> |
| public static Optional<T> OfNullable(T value) |
| { |
| if (value == null) |
| { |
| return Empty(); |
| } |
| else |
| { |
| return Of(value); |
| } |
| } |
| |
| /// <summary> |
| /// Returns <see cref="other"/> if the current <see cref="Optional{T}"/> is empty. |
| /// </summary> |
| public T OrElse(T other) |
| { |
| if (IsPresent()) |
| { |
| return Value; |
| } |
| else |
| { |
| return other; |
| } |
| } |
| |
| /// <summary> |
| /// Returns true if the current <see cref="Optional{T}"/> is empty, false otherwise. |
| /// For nullable <see cref="T"/>, the <see cref="Optional{T}"/> is empty if <see cref="Value"/> is null. |
| /// For non-nullable <see cref="T"/>, the <see cref="Optional{T}"/> is empty if <see cref="Optional{T}"/> |
| /// is created with <see cref="Empty"/>. |
| /// </summary> |
| public bool IsPresent() |
| { |
| return _isSet && _value != null; |
| } |
| |
| /// <summary> |
| /// Tests the equality of the underlying <see cref="Value"/>. |
| /// </summary> |
| public override bool Equals(object obj) |
| { |
| if (this == obj) |
| { |
| return true; |
| } |
| if (obj == null || obj.GetType() != this.GetType()) |
| { |
| return false; |
| } |
| Optional<T> optional = (Optional<T>)obj; |
| if (_value != null ? !_value.Equals(optional.Value) : optional.Value != null) |
| { |
| return false; |
| } |
| return true; |
| } |
| |
| /// <summary> |
| /// Gets the hashcode of the underlying <see cref="Value"/>. |
| /// </summary> |
| /// <returns></returns> |
| public override int GetHashCode() |
| { |
| return _value != null ? _value.GetHashCode() : 0; |
| } |
| |
| public override string ToString() |
| { |
| return "Optional{value=" + _value + "}"; |
| } |
| } |
| } |