| /******************************************************************************* |
| * Copyright (c) 2009 IBM Corporation and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * IBM Corporation - initial API and implementation |
| *******************************************************************************/ |
| |
| package org.eclipse.e4.core.services.context; |
| |
| import org.eclipse.e4.core.services.context.spi.ContextFunction; |
| |
| /** |
| * A context function encapsulates evaluation of some code within an {@link IEclipseContext}. |
| * The result of the function must be derived purely from the provided arguments and |
| * context objects, and must be free from side-effects other than the function's return value. |
| * In particular, the function must be idempotent - subsequent invocations of the same function |
| * with the same inputs must produce the same result. |
| * <p> |
| * A common use for context functions is as a place holder for an object that has not yet |
| * been created. These place holders can be stored as values in an {@link IEclipseContext}, |
| * allowing the concrete value they represent to be computed lazily only when requested. |
| * </p> |
| * |
| * @see IEclipseContext#set(String, Object) |
| * @noimplement This interface is not intended to be implemented by clients. Function |
| * implementations must subclass {@link ContextFunction} instead. |
| */ |
| public interface IContextFunction { |
| /** |
| * Evaluates the function based on the provided arguments and context to produce |
| * a consistent result. |
| * |
| * @param context The context in which to perform the value computation. |
| * @param arguments The arguments required to compute the value, or |
| * <code>null</code> if no arguments are applicable |
| * @return The concrete value. |
| */ |
| public Object compute(IEclipseContext context, Object[] arguments); |
| |
| } |
