/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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
    *
    *      https://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 org.apache.commons.jexl3;
  
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashSet;
  import java.util.Objects;
  import java.util.Set;
  import java.util.TreeSet;
  import java.util.function.Predicate;
  
  /**
   * A set of language feature options.
   * <p>
   * These control <em>syntactical</em> constructs that will throw JexlException.Feature exceptions (a
   * subclass of JexlException.Parsing) when disabled.
   * </p>
   * <p>It is recommended to be explicit in choosing the features you need rather than rely on the default
   * constructor: the 2 convenience methods {@link JexlFeatures#createNone()} and {@link JexlFeatures#createAll()}
   * are the recommended starting points to selectively enable or disable chosen features.</p>
   * <ul>
   * <li>Registers: register syntax (#number), used internally for {g,s}etProperty</li>
   * <li>Reserved Names: a set of reserved variable names that cannot be used as local variable (or parameter) names</li>
   * <li>Global Side Effect : assigning/modifying values on global variables (=, += , -=, ...)</li>
   * <li>Lexical: lexical scope, prevents redefining local variables</li>
   * <li>Lexical Shade: local variables shade globals, prevents confusing a global variable with a local one</li>
   * <li>Side Effect : assigning/modifying values on any variables or left-value</li>
   * <li>Constant Array Reference: ensures array references only use constants;they should be statically solvable.</li>
   * <li>New Instance: creating an instance using new(...)</li>
   * <li>Loops: loop constructs (while(true), for(...))</li>
   * <li>Lambda: function definitions (()-&gt;{...}, function(...) ).</li>
   * <li>Method calls: calling methods (obj.method(...) or obj['method'](...)); when disabled, leaves function calls
   * - including namespace prefixes - available</li>
   * <li>Structured literals: arrays, lists, maps, sets, ranges</li>
   * <li>Pragma: pragma construct as in {@code #pragma x y}</li>
   * <li>Annotation: @annotation statement;</li>
   * <li>Thin-arrow: use the thin-arrow, ie {@code ->} for lambdas as in {@code x -> x + x}</li>
   * <li>Fat-arrow: use the  fat-arrow, ie {@code =>} for lambdas as in {@code x => x + x}
   * <li>Namespace pragma: whether the {@code #pragma jexl.namespace.ns namespace} syntax is allowed</li>
   * <li>Namespace identifier: whether the {@code ns:fun(...)} parser treats the ns:fun as one identifier, no spaces allowed</li>
   * <li>Import pragma: whether the {@code #pragma jexl.import fully.qualified.class.name} syntax is allowed</li>
   * <li>Comparator names: whether the comparator operator names can be used (as in {@code gt} for &gt;,
   * {@code lt} for &lt;, ...)</li>
   * <li>Pragma anywhere: whether pragma, that are <em>not</em> statements and handled before execution begins,
   * can appear anywhere in the source or before any statements - ie at the beginning of a script.</li>
   * <li>Const Capture: whether variables captured by lambdas are read-only (aka const, same as Java) or read-write.</li>
   * <li>Reference Capture: whether variables captured by lambdas are pass-by-reference or pass-by-value.</li>
   * </ul>
   *
   * @since 3.2
   */
  public final class JexlFeatures {
  
      /** The false predicate. */
      public static final Predicate<String> TEST_STR_FALSE = s -> false;
  
      /** Te feature names (for toString()). */
      private static final String[] F_NAMES = {
          "register", "reserved variable", "local variable", "assign/modify",
          "global assign/modify", "array reference", "create instance", "loop", "function",
          "method call", "set/map/array literal", "pragma", "annotation", "script", "lexical", "lexicalShade",
          "thin-arrow", "fat-arrow", "namespace pragma", "namespace identifier", "import pragma", "comparator names", "pragma anywhere",
          "const capture", "ref capture", "ambiguous statement"
      };
  
      /** Registers feature ordinal. */
      private static final int REGISTER = 0;
  
      /** Reserved future feature ordinal (unused as of 3.3.1). */
      public static final int RESERVED = 1;
  
      /** Locals feature ordinal. */
      public static final int LOCAL_VAR = 2;
  
      /** Side effects feature ordinal. */
      public static final int SIDE_EFFECT = 3;
  
      /** Global side effects feature ordinal. */
      public static final int SIDE_EFFECT_GLOBAL = 4;
  
      /** Expressions allowed in array reference ordinal. */
      public static final int ARRAY_REF_EXPR = 5;
  
     /** New-instance feature ordinal. */
     public static final int NEW_INSTANCE = 6;
 
     /** Loops feature ordinal. */
     public static final int LOOP = 7;
 
     /** Lambda feature ordinal. */
     public static final int LAMBDA = 8;
 
     /** Lambda feature ordinal. */
     public static final int METHOD_CALL = 9;
 
     /** Structured literal feature ordinal. */
     public static final int STRUCTURED_LITERAL = 10;
 
     /** Pragma feature ordinal. */
     public static final int PRAGMA = 11;
 
     /** Annotation feature ordinal. */
     public static final int ANNOTATION = 12;
 
     /** Script feature ordinal. */
     public static final int SCRIPT = 13;
 
     /** Lexical feature ordinal. */
     public static final int LEXICAL = 14;
 
     /** Lexical shade feature ordinal. */
     public static final int LEXICAL_SHADE = 15;
 
     /** Thin-arrow lambda syntax. */
     public static final int THIN_ARROW = 16;
 
     /** Fat-arrow lambda syntax. */
     public static final int FAT_ARROW = 17;
 
     /** Namespace pragma feature ordinal. */
     public static final int NS_PRAGMA = 18;
 
     /** Namespace syntax as an identifier (no space). */
     public static final int NS_IDENTIFIER = 19;
 
     /** Import pragma feature ordinal. */
     public static final int IMPORT_PRAGMA = 20;
 
     /** Comparator names (legacy) syntax. */
     public static final int COMPARATOR_NAMES = 21;
 
     /** The pragma anywhere feature ordinal. */
     public static final int PRAGMA_ANYWHERE = 22;
 
     /** Captured variables are const. */
     public static final int CONST_CAPTURE = 23;
 
     /** Captured variables are reference. */
     public static final int REF_CAPTURE = 24;
 
     /** Ambiguous or strict statement allowed. */
     public static final int AMBIGUOUS_STATEMENT = 25;
 
     /** Bad naming, use AMBIGUOUS_STATEMENT.
      * @deprecated 3.6
      */
     @Deprecated
     public static final int STRICT_STATEMENT = 25;
 
     /**
      * All features.
      * Ensure this is updated if additional features are added.
      */
     private static final long ALL_FEATURES = (1L << AMBIGUOUS_STATEMENT + 1) - 1L; // MUST REMAIN PRIVATE
 
     /**
      * The default features flag mask.
      * <p>Meant for compatibility with scripts written before 3.3.1</p>
      */
     private static final long DEFAULT_FEATURES = // MUST REMAIN PRIVATE
         1L << LOCAL_VAR
         | 1L << SIDE_EFFECT
         | 1L << SIDE_EFFECT_GLOBAL
         | 1L << ARRAY_REF_EXPR
         | 1L << NEW_INSTANCE
         | 1L << LOOP
         | 1L << LAMBDA
         | 1L << METHOD_CALL
         | 1L << STRUCTURED_LITERAL
         | 1L << PRAGMA
         | 1L << ANNOTATION
         | 1L << SCRIPT
         | 1L << THIN_ARROW
         | 1L << NS_PRAGMA
         | 1L << IMPORT_PRAGMA
         | 1L << COMPARATOR_NAMES
         | 1L << PRAGMA_ANYWHERE;
 
     /**
      * The canonical scripting (since 3.3.1) features flag mask based on the original default.
      * <p>Adds lexical, lexical-shade and const-capture but removes comparator-names and pragma-anywhere</p>
      */
     private static final long SCRIPT_FEATURES = // MUST REMAIN PRIVATE
         (DEFAULT_FEATURES
         | 1L << LEXICAL
         | 1L << LEXICAL_SHADE
         | 1L << CONST_CAPTURE) // these parentheses are necessary :-)
         & ~(1L << COMPARATOR_NAMES)
         & ~(1L << PRAGMA_ANYWHERE);
 
     /**
      * Protected future syntactic elements.
      * <p><em>class, jexl, $jexl</em></p>
      *
      * @since 3.3.1
      */
     private static final Set<String> RESERVED_WORDS =
         Collections.unmodifiableSet(new HashSet<>(Arrays.asList("class", "jexl", "$jexl")));
 
     /*
      * *WARNING*
      * Static fields may be inlined by the Java compiler, so their _values_ effectively form part of the external API.
      * Classes that reference them need to be recompiled to pick up new values.
      * This means that changes in value are not binary compatible.
      * Such fields must be private or problems may occur.
      */
 
      /**
      * Creates an all features enabled set.
      *
      * @return a new instance of all features set
      * @since 3.3.1
      */
     public static JexlFeatures createAll() {
         return new JexlFeatures(ALL_FEATURES, null, null);
     }
 
     /**
      * Creates a default features set suitable for basic but complete scripting needs.
      * <p>Maximizes compatibility with older version scripts (before 3.3), new projects should
      * use {@link JexlFeatures#createScript()} or equivalent features as a base.</p>
      * <p>The following scripting features are enabled:</p>
      * <ul>
      *   <li>local variable, {@link JexlFeatures#supportsLocalVar()}</li>
      *   <li>side effect, {@link JexlFeatures#supportsSideEffect()}</li>
      *   <li>global side effect, {@link JexlFeatures#supportsSideEffectGlobal()}</li>
      *   <li>array reference expression, {@link JexlFeatures#supportsStructuredLiteral()}</li>
      *   <li>new instance, {@link JexlFeatures#supportsNewInstance()} </li>
      *   <li>loop, {@link JexlFeatures#supportsLoops()}</li>
      *   <li>lambda, {@link JexlFeatures#supportsLambda()}</li>
      *   <li>method call, {@link JexlFeatures#supportsMethodCall()}</li>
      *   <li>structured literal, {@link JexlFeatures#supportsStructuredLiteral()}</li>
      *   <li>pragma, {@link JexlFeatures#supportsPragma()}</li>
      *   <li>annotation, {@link JexlFeatures#supportsAnnotation()}</li>
      *   <li>script, {@link JexlFeatures#supportsScript()}</li>
      *   <li>comparator names,  {@link JexlFeatures#supportsComparatorNames()}</li>
      *   <li>namespace pragma,  {@link JexlFeatures#supportsNamespacePragma()}</li>
      *   <li>import pragma, {@link JexlFeatures#supportsImportPragma()}</li>
      *   <li>pragma anywhere, {@link JexlFeatures#supportsPragmaAnywhere()}</li>
      * </ul>
      *
      * @return a new instance of a default scripting features set
      * @since 3.3.1
      */
     public static JexlFeatures createDefault() {
         return new JexlFeatures(DEFAULT_FEATURES, null, null);
     }
 
     /**
      * Creates an empty feature set.
      * <p>This is the strictest base-set since no feature is allowed, suitable as-is only
      * for the simplest expressions.</p>
      *
      * @return a new instance of an empty features set
      * @since 3.3.1
      */
     public static JexlFeatures createNone() {
         return new JexlFeatures(0L, null, null);
     }
 
     /**
      * The modern scripting features set.
      * <p>This is the recommended set for new projects.</p>
      * <p>All default features with the following differences:</p>
      * <ul>
      * <li><em>disable</em> pragma-anywhere, {@link JexlFeatures#supportsPragmaAnywhere()}</li>
      * <li><em>disable</em> comparator-names, {@link JexlFeatures#supportsComparatorNames()}</li>
      * <li><em>enable</em> lexical, {@link JexlFeatures#isLexical()}</li>
      * <li><em>enable</em> lexical-shade, {@link JexlFeatures#isLexicalShade()} </li>
      * <li><em>enable</em> const-capture, {@link JexlFeatures#supportsConstCapture()}</li>
      * </ul>
      * <p>It also adds a set of reserved words to enable future unencumbered syntax evolution:
      * <em>try, catch, throw, finally, switch, case, default, class, instanceof</em>
      * </p>
      *
      * @return a new instance of a modern scripting features set
      * @since 3.3.1
      */
     public static JexlFeatures createScript() {
         return new JexlFeatures(SCRIPT_FEATURES, RESERVED_WORDS, null);
     }
 
     /**
      * The text corresponding to a feature code.
      *
      * @param feature the feature number
      * @return the feature name
      */
     public static String stringify(final int feature) {
         return feature >= 0 && feature < F_NAMES.length ? F_NAMES[feature] : "unsupported feature";
     }
 
     /** The feature flags. */
     private long flags;
 
     /** The set of reserved names, aka global variables that cannot be masked by local variables or parameters. */
     private Set<String> reservedNames;
 
     /** The namespace names. */
     private Predicate<String> nameSpaces;
 
     /**
      * Creates default instance, equivalent to the result of calling the preferred alternative
      * {@link JexlFeatures#createDefault()}
      */
     public JexlFeatures() {
         this(DEFAULT_FEATURES, null, null);
     }
 
     /**
      * Copy constructor.
      *
      * @param features the feature to copy from
      */
     public JexlFeatures(final JexlFeatures features) {
         this(features.flags, features.reservedNames, features.nameSpaces);
     }
 
     /**
      * An all member constructor for derivation.
      * <p>Not respecting immutability or thread-safety constraints for this class constructor arguments will
      * likely result in unexpected behavior.</p>
      *
      * @param f flag
      * @param r reserved variable names; must be an immutable Set or thread-safe (concurrent or synchronized set)
      * @param n namespace predicate; must be stateless or thread-safe
      */
     protected JexlFeatures(final long f, final Set<String> r, final Predicate<String> n) {
         this.flags = f;
         this.reservedNames = r == null? Collections.emptySet() : r;
         this.nameSpaces = n == null? TEST_STR_FALSE : n;
     }
 
     /**
      * Sets whether annotation constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic annotation constructs (@annotation)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures annotation(final boolean flag) {
         setFeature(ANNOTATION, flag);
         return this;
     }
 
     /**
      * Sets whether array references expressions are enabled.
      * <p>
      * When disabled, parsing a script/expression using 'obj[ ref ]' where ref is not a string or integer literal
      * will throw a parsing exception;
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures arrayReferenceExpr(final boolean flag) {
         setFeature(ARRAY_REF_EXPR, flag);
         return this;
     }
 
     /**
      * Sets whether the legacy comparison operator names syntax is enabled.
      * <p>
      * When disabled, comparison operators names (eq;ne;le;lt;ge;gt)
      * will be treated as plain identifiers.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures comparatorNames(final boolean flag) {
         setFeature(COMPARATOR_NAMES, flag);
         return this;
     }
 
     /**
      * Sets whether lambda captured-variables are constant or mutable.
      * <p>
      * When disabled, lambda-captured variables are implicitly converted to read-write local variable (let),
      * when enabled, those are implicitly converted to read-only local variables (const).
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures constCapture(final boolean flag) {
         setFeature(CONST_CAPTURE, flag);
         return this;
     }
 
     /**
      * Sets whether lambda captured-variables are references or values.
      * <p>When variables are pass-by-reference, side effects are visible from inner lexical scopes
      * to outer-scope.</p>
      * <p>
      * When disabled, lambda-captured variables use pass-by-value semantic,
      * when enabled, those use pass-by-reference semantic.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures referenceCapture(final boolean flag) {
         setFeature(REF_CAPTURE, flag);
         return this;
     }
 
     @Override
     public boolean equals(final Object obj) {
         if (this == obj) {
             return true;
         }
         if (obj == null) {
             return false;
         }
         if (getClass() != obj.getClass()) {
             return false;
         }
         final JexlFeatures other = (JexlFeatures) obj;
         if (this.flags != other.flags) {
             return false;
         }
         if (this.nameSpaces != other.nameSpaces) {
             return false;
         }
         if (!Objects.equals(this.reservedNames, other.reservedNames)) {
             return false;
         }
         return true;
     }
 
     /**
      * Sets whether fat-arrow lambda syntax is enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic fat-arrow (=&lt;)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures fatArrow(final boolean flag) {
         setFeature(FAT_ARROW, flag);
         return this;
     }
 
     /**
      * Gets a feature flag value.
      *
      * @param feature feature ordinal
      * @return true if on, false if off
      */
     private boolean getFeature(final int feature) {
         return (flags & 1L << feature) != 0L;
     }
 
     /**
      * Gets the feature flags
      *
      * @return these features&quot;s flags
      */
     public long getFlags() {
         return flags;
     }
 
     /**
      * Gets the immutable set of reserved names.
      *
      * @return the (unmodifiable) set of reserved names.
      */
     public Set<String> getReservedNames() {
         return reservedNames;
     }
 
     @Override
     public int hashCode() { //CSOFF: MagicNumber
         int hash = 3;
         hash = 53 * hash + (int) (this.flags ^ this.flags >>> 32);
         hash = 53 * hash + (this.reservedNames != null ? this.reservedNames.hashCode() : 0);
         return hash;
     }
 
     /**
      * Sets whether import pragma constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic import pragma constructs
      * (#pragma jexl.import....) will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures importPragma(final boolean flag) {
         setFeature(IMPORT_PRAGMA, flag);
         return this;
     }
 
     /**
      * Is the lexical scope feature enabled?
      *
      * @return whether lexical scope feature is enabled */
     public boolean isLexical() {
         return getFeature(LEXICAL);
     }
 
     /**
      * Is the lexical shade feature enabled?
      *
      * @return whether lexical shade feature is enabled */
     public boolean isLexicalShade() {
         return getFeature(LEXICAL_SHADE);
     }
 
     /**
      * Checks whether a name is reserved.
      *
      * @param name the name to check
      * @return true if reserved, false otherwise
      */
     public boolean isReservedName(final String name) {
         return name != null && reservedNames.contains(name);
     }
 
     /**
      * Sets whether lambda/function constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic lambda constructs (-&gt;,function)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures lambda(final boolean flag) {
         setFeature(LAMBDA, flag);
         return this;
     }
 
     /**
      * Sets whether syntactic lexical mode is enabled.
      *
      * @param flag true means syntactic lexical function scope is in effect, false implies non-lexical scoping
      * @return this features instance
      */
     public JexlFeatures lexical(final boolean flag) {
         setFeature(LEXICAL, flag);
         if (!flag) {
             setFeature(LEXICAL_SHADE, false);
         }
         return this;
     }
 
     /**
      * Sets whether syntactic lexical shade is enabled.
      *
      * @param flag true means syntactic lexical shade is in effect and implies lexical scope
      * @return this features instance
      */
     public JexlFeatures lexicalShade(final boolean flag) {
         setFeature(LEXICAL_SHADE, flag);
         if (flag) {
             setFeature(LEXICAL, true);
         }
         return this;
     }
 
     /**
      * Sets whether local variables are enabled.
      * <p>
      * When disabled, parsing a script/expression using a local variable or parameter syntax
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures localVar(final boolean flag) {
         setFeature(LOCAL_VAR, flag);
         return this;
     }
 
     /**
      * Sets whether looping constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic looping constructs (for, while)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures loops(final boolean flag) {
         setFeature(LOOP, flag);
         return this;
     }
 
     /**
      * Sets whether method calls expressions are enabled.
      * <p>
      * When disabled, parsing a script/expression using 'obj.method()'
      * will throw a parsing exception;
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures methodCall(final boolean flag) {
         setFeature(METHOD_CALL, flag);
         return this;
     }
 
     /**
      * Sets whether namespace pragma constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic namespace pragma constructs
      * (#pragma jexl.namespace....) will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures namespacePragma(final boolean flag) {
         setFeature(NS_PRAGMA, flag);
         return this;
     }
 
     /**
      * Sets whether namespace as identifier syntax is enabled.
      * <p>
      * When enabled, a namespace call must be of the form <code>ns:fun(...)</code> with no
      * spaces between the namespace name and the function.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.5.0
      */
     public JexlFeatures namespaceIdentifier(final boolean flag) {
         setFeature(NS_IDENTIFIER, flag);
         return this;
     }
 
     /**
      * Gets the declared namespaces test.
      *
      * @return the declared namespaces test.
      */
     public Predicate<String> namespaceTest() {
         return nameSpaces;
     }
 
     /**
      * Sets a test to determine namespace declaration.
      *
      * @param names the name predicate
      * @return this features instance
      */
     public JexlFeatures namespaceTest(final Predicate<String> names) {
         nameSpaces = names == null ? TEST_STR_FALSE : names;
         return this;
     }
 
     /**
      * Sets whether creating new instances is enabled.
      * <p>
      * When disabled, parsing a script/expression using 'new(...)' will throw a parsing exception;
      * using a class as functor will fail at runtime.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures newInstance(final boolean flag) {
         setFeature(NEW_INSTANCE, flag);
         return this;
     }
 
     /**
      * Sets whether pragma constructs are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic pragma constructs (#pragma)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures pragma(final boolean flag) {
         setFeature(PRAGMA, flag);
         if (!flag) {
             setFeature(NS_PRAGMA, false);
             setFeature(IMPORT_PRAGMA, false);
         }
         return this;
     }
 
     /**
      * Sets whether pragma constructs can appear anywhere in the code.
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures pragmaAnywhere(final boolean flag) {
         setFeature(PRAGMA_ANYWHERE, flag);
         return this;
     }
 
     /**
      * Sets whether register are enabled.
      * <p>
      * This is mostly used internally during execution of JexlEngine.{g,s}etProperty.
      * </p>
      * <p>
      * When disabled, parsing a script/expression using the register syntax will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures register(final boolean flag) {
         setFeature(REGISTER, flag);
         return this;
     }
 
     /**
      * Sets a collection of reserved r precluding those to be used as local variables or parameter r.
      *
      * @param names the r to reserve
      * @return this features instance
      */
     public JexlFeatures reservedNames(final Collection<String> names) {
         if (names == null || names.isEmpty()) {
             reservedNames = Collections.emptySet();
         } else {
             reservedNames = Collections.unmodifiableSet(new TreeSet<>(names));
         }
         return this;
     }
 
     /**
      * Sets whether scripts constructs are enabled.
      * <p>
      * When disabled, parsing a script using syntactic script constructs (statements, ...)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures script(final boolean flag) {
         setFeature(SCRIPT, flag);
         return this;
     }
 
     /**
      * Sets a feature flag.
      *
      * @param feature the feature ordinal
      * @param flag    turn-on, turn off
      */
     private void setFeature(final int feature, final boolean flag) {
         if (flag) {
             flags |= 1L << feature;
         } else {
             flags &= ~(1L << feature);
         }
     }
 
     /**
      * Sets whether statements can be ambiguous.
      * <p>
      * When enabled, the semicolumn is not required between expressions that otherwise are considered
      * ambiguous. The default will report ambiguity in cases like <code>if (true) { x 5 }</code> considering this
      * may be missing an operator or that the intent is not clear.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures ambiguousStatement(final boolean flag) {
         setFeature(AMBIGUOUS_STATEMENT, flag);
         return this;
     }
 
     /**
      * Checks whether statements can be ambiguous.
      * <p>
      * When enabled, the semicolumn is not required between expressions that otherwise are considered
      * ambiguous. The default will report ambiguity in cases like <code>if (true) { x 5 }</code> considering this
      * may be missing an operator or that the intent is not clear.
      * </p>
      *
      * @return true if statements can be ambiguous, false otherwise
      */
     public boolean supportsAmbiguousStatement() {
         return getFeature(AMBIGUOUS_STATEMENT);
     }
 
     /**
      * Sets whether side effect expressions are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactical constructs modifying variables
      * or members will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures sideEffect(final boolean flag) {
         setFeature(SIDE_EFFECT, flag);
         return this;
     }
 
     /**
      * Sets whether side effect expressions on global variables (aka non-local) are enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactical constructs modifying variables
      * <em>including all potentially ant-ish variables</em> will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures sideEffectGlobal(final boolean flag) {
         setFeature(SIDE_EFFECT_GLOBAL, flag);
         return this;
     }
 
     /**
      * Sets whether array/map/set literal expressions are enabled.
      * <p>
      * When disabled, parsing a script/expression creating one of these literals
      * will throw a parsing exception;
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      */
     public JexlFeatures structuredLiteral(final boolean flag) {
         setFeature(STRUCTURED_LITERAL, flag);
         return this;
     }
 
     /**
      * Does the engine support annotations?
      *
      * @return true if annotation are enabled, false otherwise
      */
     public boolean supportsAnnotation() {
         return getFeature(ANNOTATION);
     }
 
     /**
      * Does the engine support array references which contain method call expressions?
      *
      * @return true if array references can contain method call expressions, false otherwise
      */
     public boolean supportsArrayReferenceExpr() {
         return getFeature(ARRAY_REF_EXPR);
     }
 
     /**
      * Does the engine support legacy comparison operator names syntax?
      *
      * @return true if legacy comparison operator names syntax is enabled, false otherwise
      * @since 3.3
      */
     public boolean supportsComparatorNames() {
         return getFeature(COMPARATOR_NAMES);
     }
 
     /**
      * Does the engine support lambda captured-variables as const?
      *
      * @return true if lambda captured-variables are const, false otherwise
      */
     public boolean supportsConstCapture() {
         return getFeature(CONST_CAPTURE);
     }
 
     /**
      * Does the engine support lambda captured-variables as references?
      *
      * @return true if lambda captured-variables are references, false otherwise
      */
     public boolean supportsReferenceCapture() {
         return getFeature(REF_CAPTURE);
     }
 
     /**
      * Does the engine support expressions (aka not scripts)
      *
      * @return true if expressions (aka not scripts) are enabled, false otherwise
      */
     public boolean supportsExpression() {
         return !getFeature(SCRIPT);
     }
 
     /**
      * Does the engine support fat-arrow lambda syntax?
      *
      * @return true if fat-arrow lambda syntax is enabled, false otherwise
      * @since 3.3
      */
     public boolean supportsFatArrow() {
         return getFeature(FAT_ARROW);
     }
 
     /**
      * Does the engine support import pragma?
      *
      * @return true if import pragma are enabled, false otherwise
      * @since 3.3
      */
     public boolean supportsImportPragma() {
         return getFeature(IMPORT_PRAGMA);
     }
 
     /**
      * Does the engine support lambdas?
      *
      * @return true if lambda are enabled, false otherwise
      */
     public boolean supportsLambda() {
         return getFeature(LAMBDA);
     }
 
     /**
      * Is local variables syntax enabled?
      *
      * @return true if local variables syntax is enabled
      */
     public boolean supportsLocalVar() {
         return getFeature(LOCAL_VAR);
     }
 
     /**
      * Are loops enabled?
      *
      * @return true if loops are enabled, false otherwise
      */
     public boolean supportsLoops() {
         return getFeature(LOOP);
     }
 
     /**
      * Can array references contain expressions?
      *
      * @return true if array references can contain expressions, false otherwise
      */
     public boolean supportsMethodCall() {
         return getFeature(METHOD_CALL);
     }
 
     /**
      * Is namespace pragma enabled?
      *
      * @return true if namespace pragma are enabled, false otherwise
      * @since 3.3
      */
     public boolean supportsNamespacePragma() {
         return getFeature(NS_PRAGMA);
     }
 
     /**
      * Is namespace identifier syntax enabled?
      *
      * @return true if namespace identifier syntax is enabled, false otherwise
      * @since 3.5.0
      */
     public boolean supportsNamespaceIdentifier() {
         return getFeature(NS_IDENTIFIER);
     }
 
     /**
      * Is creating new instances enabled?
      *
      * @return true if creating new instances is enabled, false otherwise
      */
     public boolean supportsNewInstance() {
         return getFeature(NEW_INSTANCE);
     }
 
     /**
      * Is the namespace pragma enabled?
      *
      * @return true if namespace pragma are enabled, false otherwise
      */
     public boolean supportsPragma() {
         return getFeature(PRAGMA);
     }
 
     /**
      * Can pragma constructs appear anywhere in the code?
      *
      * @return true if pragma constructs can appear anywhere in the code, false otherwise
      * @since 3.3
      */
     public boolean supportsPragmaAnywhere() {
         return getFeature(PRAGMA_ANYWHERE);
     }
 
     /**
      * Is register syntax enabled?
      *
      * @return true if register syntax is enabled
      */
     public boolean supportsRegister() {
         return getFeature(REGISTER);
     }
 
     /**
      * Are scripts enabled?
      *
      * @return true if scripts are enabled, false otherwise
      */
     public boolean supportsScript() {
         return getFeature(SCRIPT);
     }
 
     /**
      * Are side effects enabled?
      *
      * @return true if side effects are enabled, false otherwise
      */
     public boolean supportsSideEffect() {
         return getFeature(SIDE_EFFECT);
     }
 
     /**
      * Can global variables be assigned?
      *
      * @return true if global variables can be assigned
      */
     public boolean supportsSideEffectGlobal() {
         return getFeature(SIDE_EFFECT_GLOBAL);
     }
 
     /**
      * Are array/map/set literal expressions supported?
      *
      * @return true if array/map/set literal expressions are supported, false otherwise
      */
     public boolean supportsStructuredLiteral() {
         return getFeature(STRUCTURED_LITERAL);
     }
 
     /**
      * Is thin-arrow lambda syntax enabled?
      *
      * @return true if thin-arrow lambda syntax is enabled, false otherwise
      * @since 3.3
      */
     public boolean supportsThinArrow() {
         return getFeature(THIN_ARROW);
     }
 
     /**
      * Sets whether thin-arrow lambda syntax is enabled.
      * <p>
      * When disabled, parsing a script/expression using syntactic thin-arrow (-&lt;)
      * will throw a parsing exception.
      * </p>
      *
      * @param flag true to enable, false to disable
      * @return this features instance
      * @since 3.3
      */
     public JexlFeatures thinArrow(final boolean flag) {
         setFeature(THIN_ARROW, flag);
         return this;
     }
 }