package com.bigdata.bop;
import java.util.Map;
/**
* Operator causes a variable to be bound to the result of its evaluation as a
* side-effect.
*
* @author thompsonbry
*/
public class Bind<E> extends ImmutableBOp implements IValueExpression<E>, IBind<E> {
/**
*
*/
private static final long serialVersionUID = 1L;
/**
* Constructor required for {@link com.bigdata.bop.BOpUtility#deepCopy(FilterNode)}.
*/
public Bind(Bind<E> op) {
super(op);
}
/**
* @param var
* The {@link IVariable} which will be bound to the result of
* evaluating the associated value expression.
* @param expr
* The {@link IValueExpression} to be evaluated.
*/
public Bind(IVariable<E> var, IValueExpression<E> expr) {
this(new BOp[] { var, expr }, null/* annotations */);
}
/**
* Required shallow copy constructor.
* @param args
* @param annotations
*/
public Bind(BOp[] args, Map<String, Object> annotations) {
super(args, annotations);
}
/**
* Return the variable which will be bound to the result of evaluating the
* associated value expression.
*/
@SuppressWarnings("unchecked")
public IVariable<? extends E> getVar() {
return (IVariable<? extends E>) get(0);
}
/**
* Return the value expression.
*/
@SuppressWarnings("unchecked")
public IValueExpression<E> getExpr() {
return (IValueExpression<E>) get(1);
}
public E get(final IBindingSet bindingSet) {
final IVariable<? extends E> var = getVar();
final IValueExpression<E> expr = getExpr();
// evaluate the value expression.
final E val = expr.get(bindingSet);
if(val==null){
return null;
}
// bind the variable as a side-effect.
bindingSet.set(var, new Constant<E>(val));
// return the evaluated value
return val;
}
}