com.metamx.common.guava.Yielder Maven / Gradle / Ivy
/*
* Copyright 2011,2012 Metamarkets Group Inc.
*
* Licensed 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 com.metamx.common.guava;
import java.io.Closeable;
/**
* A Yielder is an object that tries to act like the yield() command/continuations in other languages. It's not
* necessarily good at this job, but it works. I think.
*
* Essentially, you can think of a Yielder as a linked list of items where the Yielder gives you access to the current
* head via get() and it will give you another Yielder representing the next item in the chain via next(). A Yielder
* that isDone() may return anything from both get() and next(), there is no contract and depending on those return
* values will likely lead to bugs.
*
* Once next is called, there is no guarantee and no requirement that references to old Yielder objects will continue
* to obey the contract.
*
* Yielders are Closeable and *must* be closed in order to prevent resource leaks. Once close() is called, the behavior
* of the whole chain of Yielders is undefined.
*/
public interface Yielder extends Closeable
{
/**
* Gets the object currently held by this Yielder. Can be called multiple times as long as next() is not called.
*
* Once next() is called on this Yielder object, all further operations on this object are undefined.
*
* @return the currently yielded object, null if done
*/
public T get();
/**
* Gets the next Yielder in the chain. The argument is used as the accumulator value to pass along to start the
* accumulation until the next yield() call or iteration completes.
*
* Once next() is called on this Yielder object, all further operations on this object are undefined.
*
* @param initValue the initial value to pass along to start the accumulation until the next yield() call or
* iteration completes.
* @return the next Yielder in the chain, or undefined if done
*/
public Yielder next(T initValue);
/**
* Returns true if this is the last Yielder in the chain. A Yielder that isDone() may return anything
* from both get() and next(), there is no contract and depending on those return values will likely lead to bugs.
* It will probably break your code to call next() on a Yielder that is done and expect something good from it.
*
* Once next() is called on this Yielder object, all further operations on this object are undefined.
*
* @return true if this is the last Yielder in the chain, false otherwise
*/
public boolean isDone();
}