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/*******************************************************************************
* Copyright (c) 2000, 2008 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.core.expressions;
import org.eclipse.core.runtime.CoreException;
/**
* An evaluation context is used to manage a set of objects needed during
* XML expression evaluation. A context has a parent context, can manage
* a set of named variables and has a default variable. The default variable
* is used during XML expression evaluation if no explicit variable is
* referenced.
* <p>
* This interface is not intended to be implemented by clients. Clients
* are allowed to instantiate <code>EvaluationContext</code>.
* </p>
*
* @since 3.0
*
* @noimplement This interface is not intended to be implemented by clients.
* @noextend This interface is not intended to be extended by clients.
*/
public interface IEvaluationContext {
/**
* Represents the value used by variables that exist but are not defined
* in a evaluation context. When tested by the 'with' expression, <code>false</code>
* will be returned.
*
* @since 3.4
*/
Object UNDEFINED_VARIABLE = new Object();
/**
* Returns the parent context or <code>null</code> if
* this is the root of the evaluation context hierarchy.
*
* @return the parent evaluation context or <code>null</code>
*/
IEvaluationContext getParent();
/**
* Returns the root evaluation context.
*
* @return the root evaluation context
*/
IEvaluationContext getRoot();
/**
* Specifies whether this evaluation context allows activation
* of plug-ins for testers used in the expression tree. To actual
* trigger the plug-in loading this flag has to be set to <code>
* true</code> and the actual test expression must have the
* attribute <code>forcePluginActivation</code> set to <code>
* true</code> as well.
*
* @param value whether this evaluation context allows plug-in activation
* @since 3.2
*/
void setAllowPluginActivation(boolean value);
/**
* Returns whether this evaluation context supports plug-in
* activation. If not set via {@link #setAllowPluginActivation(boolean)}
* the parent value is returned. If no parent is set <code>false</code>
* is returned.
*
* @return whether plug-in activation is supported or not
* @since 3.2
*/
boolean getAllowPluginActivation();
/**
* Returns the default variable.
*
* @return the default variable or <code>null</code> if
* no default variable is managed.
*/
Object getDefaultVariable();
/**
* Adds a new named variable to this context. If a variable
* with the name already exists the new one overrides the
* existing one.
*
* @param name the variable's name
* @param value the variable's value
*/
void addVariable(String name, Object value);
/**
* Removes the variable managed under the given name
* from this evaluation context.
*
* @param name the variable's name
* @return the currently stored value or <code>null</code> if
* the variable doesn't exist
*/
Object removeVariable(String name);
/**
* Returns the variable managed under the given name.
*
* @param name the variable's name
* @return the variable's value or <code>null</code> if the content
* doesn't manage a variable with the given name
*/
Object getVariable(String name);
/**
* Resolves a variable for the given name and arguments. This
* method can be used to dynamically resolve variable such as
* plug-in descriptors, resources, etc. The method is used
* by the <code>resolve</code> expression.
*
* @param name the variable to resolve
* @param args an object array of arguments used to resolve the
* variable
* @return the variable's value or <code>null</code> if no variable
* can be resolved for the given name and arguments
* @exception CoreException if an errors occurs while resolving
* the variable
*/
Object resolveVariable(String name, Object[] args) throws CoreException;
}
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