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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 Saxonica Limited
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.expr;
import net.sf.saxon.expr.parser.*;
import net.sf.saxon.om.GroundedValue;
import net.sf.saxon.om.Item;
import net.sf.saxon.trace.ExpressionPresenter;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.type.AtomicType;
import net.sf.saxon.value.Cardinality;
import java.util.ArrayList;
import java.util.List;
/**
* Binary Expression: a numeric or boolean expression consisting of the
* two operands and an operator
*/
public abstract class BinaryExpression extends Expression {
private final Operand lhs;
private final Operand rhs;
protected int operator; // represented by the token number from class Tokenizer
/**
* Create a binary expression identifying the two operands and the operator
*
* @param p0 the left-hand operand
* @param op the operator, as a token returned by the Tokenizer (e.g. Token.AND)
* @param p1 the right-hand operand
*/
public BinaryExpression(Expression p0, int op, Expression p1) {
operator = op;
// p0.verifyParentPointers();
// p1.verifyParentPointers();
lhs = new Operand(this, p0, getOperandRole(0));
rhs = new Operand(this, p1, getOperandRole(1));
adoptChildExpression(p0);
adoptChildExpression(p1);
}
@Override
final public Iterable operands() {
return operandList(lhs, rhs);
}
/**
* Get the operand role
* @param arg which argument: 0 for the lhs, 1 for the rhs
* @return the operand role
*/
protected OperandRole getOperandRole(int arg) {
return OperandRole.SINGLE_ATOMIC;
}
/**
* Get the left-hand operand
* @return the left-hand operand
*/
public Operand getLhs() {
return lhs;
}
/**
* Get the left-hand operand expression
* @return the left-hand operand child expression
*/
public final Expression getLhsExpression() {
return lhs.getChildExpression();
}
/**
* Set the left-hand operand expression
* @param child the left-hand operand expression
*/
public void setLhsExpression(Expression child) {
lhs.setChildExpression(child);
}
/**
* Get the right-hand operand
* @return the right-hand operand
*/
public Operand getRhs() {
return rhs;
}
/**
* Get the right-hand operand expression
* @return the right-hand operand expression
*/
public final Expression getRhsExpression() {
return rhs.getChildExpression();
}
/**
* Set the right-hand operand expression
* @param child the right-hand operand expression
*/
public void setRhsExpression(Expression child) {
rhs.setChildExpression(child);
}
/**
* Type-check the expression. Default implementation for binary operators that accept
* any kind of operand
*/
/*@NotNull*/
@Override
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException {
resetLocalStaticProperties();
lhs.typeCheck(visitor, contextInfo);
rhs.typeCheck(visitor, contextInfo);
// if both operands are known, pre-evaluate the expression
try {
if ((getLhsExpression() instanceof Literal) && (getRhsExpression() instanceof Literal)) {
GroundedValue v = evaluateItem(visitor.getStaticContext().makeEarlyEvaluationContext()).materialize();
return Literal.makeLiteral(v, this);
}
} catch (XPathException err) {
// if early evaluation fails, suppress the error: the value might
// not be needed at run-time
}
return this;
}
/**
* Perform optimisation of an expression and its subexpressions.
* This method is called after all references to functions and variables have been resolved
* to the declaration of the function or variable, and after all type checking has been done.
*
* @param visitor an expression visitor
* @param contextItemType the static type of "." at the point where this expression is invoked.
* The parameter is set to null if it is known statically that the context item will be undefined.
* If the type of the context item is not known statically, the argument is set to
* {@link net.sf.saxon.type.Type#ITEM_TYPE}
* @return the original expression, rewritten if appropriate to optimize execution
* @throws XPathException if an error is discovered during this phase
* (typically a type error)
*/
/*@NotNull*/
@Override
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException {
lhs.optimize(visitor, contextItemType);
rhs.optimize(visitor, contextItemType);
// if both operands are known, pre-evaluate the expression
try {
Optimizer opt = visitor.obtainOptimizer();
if (opt.isOptionSet(OptimizerOptions.CONSTANT_FOLDING) &&
(getLhsExpression() instanceof Literal) && (getRhsExpression() instanceof Literal)) {
Item item = evaluateItem(visitor.getStaticContext().makeEarlyEvaluationContext());
if (item != null) {
GroundedValue v = item.materialize();
return Literal.makeLiteral(v, this);
}
}
} catch (XPathException err) {
// if early evaluation fails, suppress the error: the value might
// not be needed at run-time
}
return this;
}
/**
* Mark an expression as being "flattened". This is a collective term that includes extracting the
* string value or typed value, or operations such as simple value construction that concatenate text
* nodes before atomizing. The implication of all of these is that although the expression might
* return nodes, the identity of the nodes has no significance. This is called during type checking
* of the parent expression.
*
* @param flattened set to true if the result of the expression is atomized or otherwise turned into
* an atomic value
*/
@Override
public void setFlattened(boolean flattened) {
getLhsExpression().setFlattened(flattened);
getRhsExpression().setFlattened(flattened);
}
/**
* Get the operator
*
* @return the operator, for example {@link Token#PLUS}
*/
public int getOperator() {
return operator;
}
/**
* Determine the static cardinality. Default implementation returns [0..1] if either operand
* can be empty, or [1..1] otherwise, provided that the arguments are of atomic type. This
* caveat is necessary because the method can be called before type-checking, and a node
* or array with cardinality [1..n] might be atomized to an empty sequence.
*/
@Override
protected int computeCardinality() {
Expression lhs = getLhsExpression();
Expression rhs = getRhsExpression();
if (!Cardinality.allowsZero(lhs.getCardinality()) &&
lhs.getItemType() instanceof AtomicType &&
!Cardinality.allowsZero(rhs.getCardinality()) &&
rhs.getItemType() instanceof AtomicType) {
return StaticProperty.EXACTLY_ONE;
} else {
return StaticProperty.ALLOWS_ZERO_OR_ONE;
}
}
/**
* Determine the special properties of this expression
*
* @return {@link StaticProperty#NO_NODES_NEWLY_CREATED}. This is overridden
* for some subclasses.
*/
@Override
protected int computeSpecialProperties() {
int p = super.computeSpecialProperties();
return p | StaticProperty.NO_NODES_NEWLY_CREATED;
}
/**
* Determine whether a binary operator is commutative, that is, A op B = B op A.
*
* @param operator the operator, for example {@link Token#PLUS}
* @return true if the operator is commutative
*/
protected static boolean isCommutative(int operator) {
return operator == Token.AND ||
operator == Token.OR ||
operator == Token.UNION ||
operator == Token.INTERSECT ||
operator == Token.PLUS ||
operator == Token.MULT ||
operator == Token.EQUALS ||
operator == Token.FEQ ||
operator == Token.NE ||
operator == Token.FNE;
}
/**
* Determine whether an operator is associative, that is, ((a^b)^c) = (a^(b^c))
*
* @param operator the operator, for example {@link Token#PLUS}
* @return true if the operator is associative
*/
protected static boolean isAssociative(int operator) {
return operator == Token.AND ||
operator == Token.OR ||
operator == Token.UNION ||
operator == Token.INTERSECT ||
operator == Token.PLUS ||
operator == Token.MULT;
}
/**
* Test if one operator is the inverse of another, so that (A op1 B) is
* equivalent to (B op2 A). Commutative operators are the inverse of themselves
* and are therefore not listed here.
*
* @param op1 the first operator
* @param op2 the second operator
* @return true if the operators are the inverse of each other
*/
protected static boolean isInverse(int op1, int op2) {
return op1 != op2 && op1 == Token.inverse(op2);
}
/**
* An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
* This method indicates which of these methods is provided directly. The other methods will always be available
* indirectly, using an implementation that relies on one of the other methods.
*
* @return the implementation method, for example {@link #ITERATE_METHOD} or {@link #EVALUATE_METHOD} or
* {@link #PROCESS_METHOD}
*/
@Override
public int getImplementationMethod() {
return EVALUATE_METHOD | ITERATE_METHOD;
}
/**
* Is this expression the same as another expression?
*/
public boolean equals(Object other) {
if (other instanceof BinaryExpression && hasCompatibleStaticContext((Expression)other)) {
BinaryExpression b = (BinaryExpression) other;
Expression lhs1 = getLhsExpression();
Expression rhs1 = getRhsExpression();
Expression lhs2 = b.getLhsExpression();
Expression rhs2 = b.getRhsExpression();
if (operator == b.operator) {
if (lhs1.isEqual(lhs2) && rhs1.isEqual(rhs2)) {
return true;
}
if (isCommutative(operator) && lhs1.isEqual(rhs2) && rhs1.isEqual(lhs2)) {
return true;
}
if (isAssociative(operator) && pairwiseEqual(flattenExpression(), b.flattenExpression())) {
return true;
}
}
return isInverse(operator, b.operator) && lhs1.isEqual(rhs2) && rhs1.isEqual(lhs2);
}
return false;
}
private List flattenExpression() {
List list = new ArrayList<>();
return flattenExpression(list);
}
/**
* Flatten an expression with respect to an associative operator: for example
* the expression (a+b) + (c+d) becomes list(a,b,c,d), with the list in canonical
* order (sorted by hashCode)
*
* @param list a list provided by the caller to contain the result
* @return the list of expressions
*/
private List flattenExpression(List list) {
if (getLhsExpression() instanceof BinaryExpression &&
((BinaryExpression) getLhsExpression()).operator == operator) {
((BinaryExpression) getLhsExpression()).flattenExpression(list);
} else {
int h = getLhsExpression().hashCode();
list.add(getLhsExpression());
int i = list.size() - 1;
while (i > 0 && h > list.get(i - 1).hashCode()) {
list.set(i, list.get(i - 1));
list.set(i - 1, getLhsExpression());
i--;
}
}
if (getRhsExpression() instanceof BinaryExpression &&
((BinaryExpression) getRhsExpression()).operator == operator) {
((BinaryExpression) getRhsExpression()).flattenExpression(list);
} else {
int h = getRhsExpression().hashCode();
list.add(getRhsExpression());
int i = list.size() - 1;
while (i > 0 && h > list.get(i - 1).hashCode()) {
list.set(i, list.get(i - 1));
list.set(i - 1, getRhsExpression());
i--;
}
}
return list;
}
/**
* Compare whether two lists of expressions are pairwise equal
*
* @param a the first list of expressions
* @param b the second list of expressions
* @return true if the two lists are equal
*/
private boolean pairwiseEqual(List a, List b) {
if (a.size() != b.size()) {
return false;
}
for (int i = 0; i < a.size(); i++) {
if (!a.get(i).equals(b.get(i))) {
return false;
}
}
return true;
}
/**
* Get a hashCode for comparing two expressions. Note that this hashcode gives the same
* result for (A op B) and for (B op A), whether or not the operator is commutative.
*/
@Override
protected int computeHashCode() {
// Ensure that an operator and its inverse get the same hash code,
// so that (A lt B) has the same hash code as (B gt A)
int op = Math.min(operator, Token.inverse(operator));
return ("BinaryExpression " + op).hashCode()
^ getLhsExpression().hashCode()
^ getRhsExpression().hashCode();
}
/**
* Represent the expression as a string. The resulting string will be a valid XPath 3.0 expression
* with no dependencies on namespace bindings other than the binding of the prefix "xs" to the XML Schema
* namespace.
*
* @return the expression as a string in XPath 3.0 syntax
*/
public String toString() {
return ExpressionTool.parenthesize(getLhsExpression()) +
" " + displayOperator() + " " +
ExpressionTool.parenthesize(getRhsExpression());
}
@Override
public String toShortString() {
return parenthesize(getLhsExpression()) + " " + displayOperator() + " " + parenthesize(getRhsExpression());
}
private String parenthesize(Expression operand) {
String operandStr = operand.toShortString();
if (operand instanceof BinaryExpression &&
XPathParser.operatorPrecedence(((BinaryExpression) operand).operator) < XPathParser.operatorPrecedence(operator)) {
operandStr = "(" + operandStr + ")";
}
return operandStr;
}
/**
* Diagnostic print of expression structure. The abstract expression tree
* is written to the supplied output destination.
*
* @param out the output destination for the displayed expression tree
*/
@Override
public void export(ExpressionPresenter out) throws XPathException {
out.startElement(tag(), this);
out.emitAttribute("op", displayOperator());
explainExtraAttributes(out);
getLhsExpression().export(out);
getRhsExpression().export(out);
out.endElement();
}
/**
* Get the element name used to identify this expression in exported expression format
* @return the element name used to identify this expression
*/
protected String tag() {
return "operator";
}
/**
* Add subclass-specific attributes to the expression tree explanation. Default implementation
* does nothing; this is provided for subclasses to override.
*
* @param out the output destination for the displayed expression tree
*/
protected void explainExtraAttributes(ExpressionPresenter out) {
}
/**
* Display the operator used by this binary expression
*
* @return String representation of the operator (for diagnostic display only)
*/
protected String displayOperator() {
return Token.tokens[operator];
}
}