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Closure Compiler is a JavaScript optimizing compiler. It parses your
JavaScript, analyzes it, removes dead code and rewrites and minimizes
what's left. It also checks syntax, variable references, and types, and
warns about common JavaScript pitfalls. It is used in many of Google's
JavaScript apps, including Gmail, Google Web Search, Google Maps, and
Google Docs.
This binary checks for style issues such as incorrect or missing JSDoc
usage, and missing goog.require() statements. It does not do more advanced
checks such as typechecking.
/*
* Copyright 2010 The Closure Compiler Authors.
*
* 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.google.javascript.jscomp;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.base.Joiner;
import com.google.common.collect.ImmutableSet;
import com.google.javascript.jscomp.CodingConvention.Bind;
import com.google.javascript.rhino.IR;
import com.google.javascript.rhino.Node;
import com.google.javascript.rhino.Token;
import java.util.regex.Pattern;
/**
* A peephole optimization that minimizes code by simplifying conditional
* expressions, replacing IFs with HOOKs, replacing object constructors
* with literals, and simplifying returns.
*/
class PeepholeSubstituteAlternateSyntax
extends AbstractPeepholeOptimization {
private static final CodeGenerator REGEXP_ESCAPER =
CodeGenerator.forCostEstimation(
null /* blow up if we try to produce code */);
private final boolean late;
private static final int STRING_SPLIT_OVERHEAD = ".split('.')".length();
static final DiagnosticType INVALID_REGULAR_EXPRESSION_FLAGS =
DiagnosticType.warning(
"JSC_INVALID_REGULAR_EXPRESSION_FLAGS",
"Invalid flags to RegExp constructor: {0}");
/**
* @param late When late is false, this mean we are currently running before
* most of the other optimizations. In this case we would avoid optimizations
* that would make the code harder to analyze (such as using string splitting,
* merging statements with commas, etc). When this is true, we would
* do anything to minimize for size.
*/
PeepholeSubstituteAlternateSyntax(boolean late) {
this.late = late;
}
/**
* Tries apply our various peephole minimizations on the passed in node.
*/
@Override
@SuppressWarnings("fallthrough")
public Node optimizeSubtree(Node node) {
switch (node.getToken()) {
case ASSIGN_SUB:
return reduceSubstractionAssignment(node);
case TRUE:
case FALSE:
return reduceTrueFalse(node);
case NEW:
node = tryFoldStandardConstructors(node);
if (!node.isCall()) {
return node;
}
// Fall through on purpose because tryFoldStandardConstructors() may
// convert a NEW node into a CALL node
case CALL:
Node result = tryFoldLiteralConstructor(node);
if (result == node) {
result = tryFoldSimpleFunctionCall(node);
if (result == node) {
result = tryFoldImmediateCallToBoundFunction(node);
}
}
return result;
case RETURN:
return tryReduceReturn(node);
case COMMA:
// TODO(b/63630312): should flatten an entire comma expression in a single pass.
return trySplitComma(node);
case NAME:
return tryReplaceUndefined(node);
case ARRAYLIT:
return tryMinimizeArrayLiteral(node);
case GETPROP:
return tryMinimizeWindowRefs(node);
case TEMPLATELIT:
return tryTurnTemplateStringsToStrings(node);
case MUL:
case AND:
case OR:
case BITOR:
case BITXOR:
case BITAND:
return tryRotateAssociativeOperator(node);
default:
return node; //Nothing changed
}
}
private static final ImmutableSet BUILTIN_EXTERNS = ImmutableSet.of(
"Object",
"Array",
"Error",
"RegExp",
"Math");
private Node tryMinimizeWindowRefs(Node node) {
// Normalization needs to be done to ensure there's no shadowing. The window prefix is also
// required if the global externs are not on the window.
if (!isASTNormalized() || !areDeclaredGlobalExternsOnWindow()) {
return node;
}
checkArgument(node.isGetProp());
if (node.getFirstChild().isName()) {
Node nameNode = node.getFirstChild();
Node stringNode = node.getLastChild();
// Since normalization has run we know we're referring to the global window.
if ("window".equals(nameNode.getString())
&& BUILTIN_EXTERNS.contains(stringNode.getString())) {
Node newNameNode = IR.name(stringNode.getString());
Node parentNode = node.getParent();
newNameNode.useSourceInfoFrom(stringNode);
parentNode.replaceChild(node, newNameNode);
if (parentNode.isCall()) {
parentNode.putBooleanProp(Node.FREE_CALL, true);
}
reportChangeToEnclosingScope(parentNode);
return newNameNode;
}
}
return node;
}
private Node tryRotateAssociativeOperator(Node n) {
if (!late) {
return n;
}
// All commutative operators are also associative
checkArgument(NodeUtil.isAssociative(n.getToken()));
Node rhs = n.getLastChild();
if (n.getToken() == rhs.getToken()) {
// Transform a * (b * c) to a * b * c
Node first = n.getFirstChild().detach();
Node second = rhs.getFirstChild().detach();
Node third = rhs.getLastChild().detach();
Node newLhs = new Node(n.getToken(), first, second).useSourceInfoIfMissingFrom(n);
Node newRoot = new Node(rhs.getToken(), newLhs, third).useSourceInfoIfMissingFrom(rhs);
n.replaceWith(newRoot);
reportChangeToEnclosingScope(newRoot);
return newRoot;
} else if (NodeUtil.isCommutative(n.getToken()) && !mayHaveSideEffects(n)) {
// Transform a * (b / c) to b / c * a
Node lhs = n.getFirstChild();
while (lhs.getToken() == n.getToken()) {
lhs = lhs.getFirstChild();
}
int precedence = NodeUtil.precedence(n.getToken());
int lhsPrecedence = NodeUtil.precedence(lhs.getToken());
int rhsPrecedence = NodeUtil.precedence(rhs.getToken());
if (rhsPrecedence == precedence && lhsPrecedence != precedence) {
n.removeChild(rhs);
lhs.replaceWith(rhs);
n.addChildToBack(lhs);
reportChangeToEnclosingScope(n);
return n;
}
}
return n;
}
private Node tryFoldSimpleFunctionCall(Node n) {
checkState(n.isCall(), n);
Node callTarget = n.getFirstChild();
if (callTarget == null || !callTarget.isName()) {
return n;
}
String targetName = callTarget.getString();
switch (targetName) {
case "Boolean":
{
// Fold Boolean(a) to !!a
// http://www.ecma-international.org/ecma-262/6.0/index.html#sec-boolean-constructor-boolean-value
// and
// http://www.ecma-international.org/ecma-262/6.0/index.html#sec-logical-not-operator-runtime-semantics-evaluation
int paramCount = n.getChildCount() - 1;
// only handle the single known parameter case
if (paramCount == 1) {
Node value = n.getLastChild().detach();
Node replacement;
if (NodeUtil.isBooleanResult(value)) {
// If it is already a boolean do nothing.
replacement = value;
} else {
// Replace it with a "!!value"
replacement = IR.not(IR.not(value).srcref(n));
}
n.replaceWith(replacement);
reportChangeToEnclosingScope(replacement);
}
break;
}
case "String":
{
// Fold String(a) to '' + (a) on immutable literals,
// which allows further optimizations
//
// We can't do this in the general case, because String(a) has
// slightly different semantics than '' + (a). See
// https://blickly.github.io/closure-compiler-issues/#759
Node value = callTarget.getNext();
if (value != null && value.getNext() == null && NodeUtil.isImmutableValue(value)) {
Node addition = IR.add(IR.string("").srcref(callTarget), value.detach());
n.replaceWith(addition);
reportChangeToEnclosingScope(addition);
return addition;
}
break;
}
default:
// nothing.
break;
}
return n;
}
private Node tryFoldImmediateCallToBoundFunction(Node n) {
// Rewriting "(fn.bind(a,b))()" to "fn.call(a,b)" makes it inlinable
checkState(n.isCall());
Node callTarget = n.getFirstChild();
Bind bind = getCodingConvention()
.describeFunctionBind(callTarget, false, false);
if (bind != null) {
// replace the call target
bind.target.detach();
n.replaceChild(callTarget, bind.target);
callTarget = bind.target;
// push the parameters
addParameterAfter(bind.parameters, callTarget);
// add the this value before the parameters if necessary
if (bind.thisValue != null && !NodeUtil.isUndefined(bind.thisValue)) {
// rewrite from "fn(a, b)" to "fn.call(thisValue, a, b)"
Node newCallTarget = IR.getprop(
callTarget.cloneTree(),
IR.string("call").srcref(callTarget));
markNewScopesChanged(newCallTarget);
n.replaceChild(callTarget, newCallTarget);
markFunctionsDeleted(callTarget);
n.addChildAfter(bind.thisValue.cloneTree(), newCallTarget);
n.putBooleanProp(Node.FREE_CALL, false);
} else {
n.putBooleanProp(Node.FREE_CALL, true);
}
reportChangeToEnclosingScope(n);
}
return n;
}
private static void addParameterAfter(Node parameterList, Node after) {
if (parameterList != null) {
// push the last parameter to the head of the list first.
addParameterAfter(parameterList.getNext(), after);
after.getParent().addChildAfter(parameterList.cloneTree(), after);
}
}
private Node trySplitComma(Node n) {
if (late) {
return n;
}
Node parent = n.getParent();
Node left = n.getFirstChild();
Node right = n.getLastChild();
if (parent.isExprResult()
&& !parent.getParent().isLabel()) {
// split comma
n.detachChildren();
// Replace the original expression with the left operand.
parent.replaceChild(n, left);
// Add the right expression afterward.
Node newStatement = IR.exprResult(right);
newStatement.useSourceInfoIfMissingFrom(n);
// This modifies outside the subtree, which is not
// desirable in a peephole optimization.
parent.getParent().addChildAfter(newStatement, parent);
reportChangeToEnclosingScope(parent);
return left;
} else {
return n;
}
}
/**
* Use "void 0" in place of "undefined"
*/
private Node tryReplaceUndefined(Node n) {
// TODO(johnlenz): consider doing this as a normalization.
if (isASTNormalized()
&& NodeUtil.isUndefined(n)
&& !NodeUtil.isLValue(n)) {
Node replacement = NodeUtil.newUndefinedNode(n);
n.replaceWith(replacement);
reportChangeToEnclosingScope(replacement);
return replacement;
}
return n;
}
/**
* Reduce "return undefined" or "return void 0" to simply "return".
*
* @return The original node, maybe simplified.
*/
private Node tryReduceReturn(Node n) {
Node result = n.getFirstChild();
if (result != null) {
switch (result.getToken()) {
case VOID:
Node operand = result.getFirstChild();
if (!mayHaveSideEffects(operand)) {
n.removeFirstChild();
reportChangeToEnclosingScope(n);
}
break;
case NAME:
String name = result.getString();
if (name.equals("undefined")) {
n.removeFirstChild();
reportChangeToEnclosingScope(n);
}
break;
default:
break;
}
}
return n;
}
private static final ImmutableSet STANDARD_OBJECT_CONSTRUCTORS =
// String, Number, and Boolean functions return non-object types, whereas
// new String, new Number, and new Boolean return object types, so don't
// include them here.
ImmutableSet.of(
"Object",
"Array",
"Error"
);
/**
* Fold "new Object()" to "Object()".
*/
private Node tryFoldStandardConstructors(Node n) {
checkState(n.isNew());
if (canFoldStandardConstructors(n)) {
n.setToken(Token.CALL);
n.putBooleanProp(Node.FREE_CALL, true);
reportChangeToEnclosingScope(n);
}
return n;
}
/**
* @return Whether "new Object()" can be folded to "Object()" on {@code n}.
*/
private boolean canFoldStandardConstructors(Node n) {
// If name normalization has been run then we know that
// new Object() does in fact refer to what we think it is
// and not some custom-defined Object().
if (isASTNormalized() && n.getFirstChild().isName()) {
String className = n.getFirstChild().getString();
if (STANDARD_OBJECT_CONSTRUCTORS.contains(className)) {
return true;
}
if ("RegExp".equals(className)) {
// Fold "new RegExp()" to "RegExp()", but only if the argument is a string.
// See issue 1260.
if (n.getSecondChild() == null || n.getSecondChild().isString()) {
return true;
}
}
}
return false;
}
/**
* Replaces a new Array, Object, or RegExp node with a literal, unless the
* call is to a local constructor function with the same name.
*/
private Node tryFoldLiteralConstructor(Node n) {
checkArgument(n.isCall() || n.isNew());
Node constructorNameNode = n.getFirstChild();
Node newLiteralNode = null;
// We require the AST to be normalized to ensure that, say,
// Object() really refers to the built-in Object constructor
// and not a user-defined constructor with the same name.
if (isASTNormalized() && constructorNameNode.isName()) {
String className = constructorNameNode.getString();
if ("RegExp".equals(className)) {
// "RegExp("boo", "g")" --> /boo/g
return tryFoldRegularExpressionConstructor(n);
} else {
boolean constructorHasArgs = constructorNameNode.getNext() != null;
if ("Object".equals(className) && !constructorHasArgs) {
// "Object()" --> "{}"
newLiteralNode = IR.objectlit();
} else if ("Array".equals(className)) {
// "Array(arg0, arg1, ...)" --> "[arg0, arg1, ...]"
Node arg0 = constructorNameNode.getNext();
FoldArrayAction action = isSafeToFoldArrayConstructor(arg0);
if (action == FoldArrayAction.SAFE_TO_FOLD_WITH_ARGS ||
action == FoldArrayAction.SAFE_TO_FOLD_WITHOUT_ARGS) {
newLiteralNode = IR.arraylit();
n.removeFirstChild(); // discard the function name
Node elements = n.removeChildren();
if (action == FoldArrayAction.SAFE_TO_FOLD_WITH_ARGS) {
newLiteralNode.addChildrenToFront(elements);
}
}
}
if (newLiteralNode != null) {
n.replaceWith(newLiteralNode);
reportChangeToEnclosingScope(newLiteralNode);
return newLiteralNode;
}
}
}
return n;
}
private static enum FoldArrayAction {
NOT_SAFE_TO_FOLD, SAFE_TO_FOLD_WITH_ARGS, SAFE_TO_FOLD_WITHOUT_ARGS}
/**
* Checks if it is safe to fold Array() constructor into []. It can be
* obviously done, if the initial constructor has either no arguments or
* at least two. The remaining case may be unsafe since Array(number)
* actually reserves memory for an empty array which contains number elements.
*/
private static FoldArrayAction isSafeToFoldArrayConstructor(Node arg) {
FoldArrayAction action = FoldArrayAction.NOT_SAFE_TO_FOLD;
if (arg == null) {
action = FoldArrayAction.SAFE_TO_FOLD_WITHOUT_ARGS;
} else if (arg.getNext() != null) {
action = FoldArrayAction.SAFE_TO_FOLD_WITH_ARGS;
} else {
switch (arg.getToken()) {
case STRING:
// "Array('a')" --> "['a']"
action = FoldArrayAction.SAFE_TO_FOLD_WITH_ARGS;
break;
case NUMBER:
// "Array(0)" --> "[]"
if (arg.getDouble() == 0) {
action = FoldArrayAction.SAFE_TO_FOLD_WITHOUT_ARGS;
}
break;
case ARRAYLIT:
// "Array([args])" --> "[[args]]"
action = FoldArrayAction.SAFE_TO_FOLD_WITH_ARGS;
break;
default:
}
}
return action;
}
private Node tryFoldRegularExpressionConstructor(Node n) {
Node parent = n.getParent();
Node constructor = n.getFirstChild();
Node pattern = constructor.getNext(); // e.g. ^foobar$
Node flags = null != pattern ? pattern.getNext() : null; // e.g. gi
if (null == pattern || (null != flags && null != flags.getNext())) {
// too few or too many arguments
return n;
}
if (// is pattern folded
pattern.isString()
// make sure empty pattern doesn't fold to //
&& !"".equals(pattern.getString())
&& (null == flags || flags.isString())
// don't escape patterns with Unicode escapes since Safari behaves badly
// (read can't parse or crashes) on regex literals with Unicode escapes
&& (isEcmaScript5OrGreater()
|| !containsUnicodeEscape(pattern.getString()))) {
// Make sure that / is escaped, so that it will fit safely in /brackets/
// and make sure that no LineTerminatorCharacters appear literally inside
// the pattern.
// pattern is a string value with \\ and similar already escaped
pattern = makeForwardSlashBracketSafe(pattern);
Node regexLiteral;
if (null == flags || "".equals(flags.getString())) {
// fold to /foobar/
regexLiteral = IR.regexp(pattern);
} else {
// fold to /foobar/gi
if (!areValidRegexpFlags(flags.getString())) {
report(INVALID_REGULAR_EXPRESSION_FLAGS, flags);
return n;
}
if (!areSafeFlagsToFold(flags.getString())) {
return n;
}
n.removeChild(flags);
regexLiteral = IR.regexp(pattern, flags);
}
parent.replaceChild(n, regexLiteral);
reportChangeToEnclosingScope(parent);
return regexLiteral;
}
return n;
}
private Node reduceSubstractionAssignment(Node n) {
Node right = n.getLastChild();
if (right.isNumber()) {
if (right.getDouble() == 1) {
Node newNode = IR.dec(n.removeFirstChild(), false);
n.replaceWith(newNode);
reportChangeToEnclosingScope(newNode);
return newNode;
} else if (right.getDouble() == -1) {
Node newNode = IR.inc(n.removeFirstChild(), false);
n.replaceWith(newNode);
reportChangeToEnclosingScope(newNode);
return newNode;
}
}
return n;
}
private Node reduceTrueFalse(Node n) {
if (late) {
switch (n.getParent().getToken()) {
case EQ:
case GT:
case GE:
case LE:
case LT:
case NE:
Node number = IR.number(n.isTrue() ? 1 : 0);
n.getParent().replaceChild(n, number);
reportChangeToEnclosingScope(number);
return number;
default:
break;
}
Node not = IR.not(IR.number(n.isTrue() ? 0 : 1));
not.useSourceInfoIfMissingFromForTree(n);
n.replaceWith(not);
reportChangeToEnclosingScope(not);
return not;
}
return n;
}
private Node tryMinimizeArrayLiteral(Node n) {
boolean allStrings = true;
for (Node cur = n.getFirstChild(); cur != null; cur = cur.getNext()) {
if (!cur.isString()) {
allStrings = false;
}
}
if (allStrings) {
return tryMinimizeStringArrayLiteral(n);
} else {
return n;
}
}
private Node tryMinimizeStringArrayLiteral(Node n) {
if (!late) {
return n;
}
int numElements = n.getChildCount();
// We save two bytes per element.
int saving = numElements * 2 - STRING_SPLIT_OVERHEAD;
if (saving <= 0) {
return n;
}
String[] strings = new String[numElements];
int idx = 0;
for (Node cur = n.getFirstChild(); cur != null; cur = cur.getNext()) {
strings[idx++] = cur.getString();
}
// These delimiters are chars that appears a lot in the program therefore
// probably have a small Huffman encoding.
String delimiter = pickDelimiter(strings);
if (delimiter != null) {
String template = Joiner.on(delimiter).join(strings);
Node call = IR.call(
IR.getprop(
IR.string(template),
IR.string("split")),
IR.string("" + delimiter));
call.useSourceInfoIfMissingFromForTree(n);
n.replaceWith(call);
reportChangeToEnclosingScope(call);
return call;
}
return n;
}
private Node tryTurnTemplateStringsToStrings(Node n) {
checkState(n.isTemplateLit(), n);
if (n.getParent().isTaggedTemplateLit()) {
return n;
}
String string = getSideEffectFreeStringValue(n);
if (string == null) {
return n;
}
Node stringNode = IR.string(string).srcref(n);
n.replaceWith(stringNode);
reportChangeToEnclosingScope(stringNode);
return stringNode;
}
/**
* Find a delimiter that does not occur in the given strings
* @param strings The strings that must be separated.
* @return a delimiter string or null
*/
private static String pickDelimiter(String[] strings) {
boolean allLength1 = true;
for (String s : strings) {
if (s.length() != 1) {
allLength1 = false;
break;
}
}
if (allLength1) {
return "";
}
String[] delimiters = new String[]{" ", ";", ",", "{", "}", null};
int i = 0;
NEXT_DELIMITER: for (; delimiters[i] != null; i++) {
for (String cur : strings) {
if (cur.contains(delimiters[i])) {
continue NEXT_DELIMITER;
}
}
break;
}
return delimiters[i];
}
private static final Pattern REGEXP_FLAGS_RE = Pattern.compile("^[gmi]*$");
/**
* are the given flags valid regular expression flags?
* JavaScript recognizes several suffix flags for regular expressions,
* 'g' - global replace, 'i' - case insensitive, 'm' - multi-line.
* They are case insensitive, and JavaScript does not recognize the extended
* syntax mode, single-line mode, or expression replacement mode from Perl 5.
*/
private static boolean areValidRegexpFlags(String flags) {
return REGEXP_FLAGS_RE.matcher(flags).matches();
}
/**
* are the given flags safe to fold?
* We don't fold the regular expression if global ('g') flag is on,
* because in this case it isn't really a constant: its 'lastIndex'
* property contains the state of last execution, so replacing
* 'new RegExp('foobar','g')' with '/foobar/g' may change the behavior of
* the program if the RegExp is used inside a loop, for example.
*
* ECMAScript 5 explicitly disallows pooling of regular expression literals so
* in ECMAScript 5, {@code /foo/g} and {@code new RegExp('foo', 'g')} are
* equivalent.
* From section 7.8.5:
* "Then each time the literal is evaluated, a new object is created as if by
* the expression new RegExp(Pattern, Flags) where RegExp is the standard
* built-in constructor with that name."
*/
private boolean areSafeFlagsToFold(String flags) {
return isEcmaScript5OrGreater() || flags.indexOf('g') < 0;
}
/**
* returns a string node that can safely be rendered inside /brackets/.
*/
private static Node makeForwardSlashBracketSafe(Node n) {
String s = n.getString();
// sb contains everything in s[0:pos]
StringBuilder sb = null;
int pos = 0;
boolean isEscaped = false;
boolean inCharset = false;
for (int i = 0; i < s.length(); ++i) {
char ch = s.charAt(i);
switch (ch) {
case '\\':
isEscaped = !isEscaped;
continue;
case '/':
// Escape a literal forward slash if it is not already escaped and is
// not inside a character set.
// new RegExp('/') -> /\//
// but the following do not need extra escaping
// new RegExp('\\/') -> /\//
// new RegExp('[/]') -> /[/]/
if (!isEscaped && !inCharset) {
if (null == sb) { sb = new StringBuilder(s.length() + 16); }
sb.append(s, pos, i).append('\\');
pos = i;
}
break;
case '[':
if (!isEscaped) {
inCharset = true;
}
break;
case ']':
if (!isEscaped) {
inCharset = false;
}
break;
case '\r': case '\n': case '\u2028': case '\u2029':
// LineTerminators cannot appear raw inside a regular
// expression literal.
// They can't appear legally in a quoted string, but when
// the quoted string from
// new RegExp('\n')
// reaches here, the quoting has been removed.
// Requote just these code-points.
if (null == sb) { sb = new StringBuilder(s.length() + 16); }
if (isEscaped) {
sb.append(s, pos, i - 1);
} else {
sb.append(s, pos, i);
}
switch (ch) {
case '\r': sb.append("\\r"); break;
case '\n': sb.append("\\n"); break;
case '\u2028': sb.append("\\u2028"); break;
case '\u2029': sb.append("\\u2029"); break;
}
pos = i + 1;
break;
}
isEscaped = false;
}
if (null == sb) { return n.cloneTree(); }
sb.append(s, pos, s.length());
return IR.string(sb.toString()).srcref(n);
}
/**
* true if the JavaScript string would contain a Unicode escape when written
* out as the body of a regular expression literal.
*/
static boolean containsUnicodeEscape(String s) {
String esc = REGEXP_ESCAPER.regexpEscape(s);
for (int i = -1; (i = esc.indexOf("\\u", i + 1)) >= 0;) {
int nSlashes = 0;
while (i - nSlashes > 0 && '\\' == esc.charAt(i - nSlashes - 1)) {
++nSlashes;
}
// if there are an even number of slashes before the \ u then it is a
// Unicode literal.
if (0 == (nSlashes & 1)) { return true; }
}
return false;
}
}