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/*
* 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.
*/
package org.apache.thrift;
/**
* Implementation of the Option type pattern
*/
public abstract class Option<T> {
@SuppressWarnings("rawtypes")
private static final Option NONE = new None();
/**
* Whether the Option is defined or not
* @return
* true if the Option is defined (of type Some)
* false if the Option is not defined (of type None)
*/
public abstract boolean isDefined();
/**
* Get the value of the Option (if it is defined)
* @return the value
* @throws IllegalStateException if called on a None
*/
public abstract T get();
/**
* Get the contained value (if defined) or else return a default value
* @param other what to return if the value is not defined (a None)
* @return either the value, or other if the value is not defined
*/
public T or(T other) {
if (isDefined()) {
return get();
} else {
return other;
}
}
/**
* The None type, representing an absent value (instead of "null")
*/
public static class None<T> extends Option<T> {
public boolean isDefined() {
return false;
}
public T get() {
throw new IllegalStateException("Cannot call get() on None");
}
public String toString() {
return "None";
}
}
/**
* The Some type, representing an existence of some value
* @param <T> The type of value
*/
public static class Some<T> extends Option<T> {
private final T value;
public Some(T value) {
this.value = value;
}
public boolean isDefined() {
return true;
}
public T get() {
return value;
}
public String toString() {
return "Some(" + value + ")";
}
}
/**
* Wraps value in an Option type, depending on whether or not value is null
* @param value the value to wrap in Option
* @param <T> the type of value
* @return Some(value) if value is not null, None if value is null
*/
public static <T> Option<T> fromNullable(T value) {
if (value != null) {
return some(value);
} else {
return none();
}
}
/**
* Wrap value in a Some type (NB! value must not be null!)
* @param value the value to wrap.
* @param <T> the type of value
* @return a new Some(value)
*/
public static <T> Some<T> some(T value) {
return new Some<T>(value);
}
@SuppressWarnings("unchecked")
public static <T> None<T> none() {
return (None<T>) NONE;
}
}
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