[GitHub] dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method to check if pattern can produce empty matches
dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method
to check if pattern can produce empty matches
URL: https://github.com/apache/flink/pull/6781#discussion_r221640010
##
File path:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
##
@@ -74,6 +77,36 @@
}
}
+ /**
+* Verifies if the provided pattern can possibly generate empty match.
Example of patterns that can possibly
+* generate empty matches are: A*, A?, A* B? etc.
+*
+* @param pattern pattern to check
+* @return true if empty match could potentially match the pattern,
false otherwise
+*/
+ public static boolean canProduceEmptyMatches(final Pattern
pattern) {
+ NFAFactoryCompiler compiler = new
NFAFactoryCompiler<>(checkNotNull(pattern));
+ compiler.compileFactory();
+ State startState =
compiler.getStates().stream().filter(State::isStart).findFirst().get();
+
+ final Stack> statesToCheck = new Stack<>();
+ statesToCheck.push(startState);
+ while (!statesToCheck.isEmpty()) {
+ final State currentState = statesToCheck.pop();
+ for (StateTransition transition :
currentState.getStateTransitions()) {
+ if (transition.getAction() ==
StateTransitionAction.PROCEED) {
+ if
(transition.getTargetState().isFinal()) {
+ return true;
+ } else {
+
statesToCheck.push(transition.getTargetState());
Review comment:
Theoretically yes, practically compiler won't produce such graph as of now.
Do you think I should be defensive though?
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[GitHub] dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method to check if pattern can produce empty matches
dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method
to check if pattern can produce empty matches
URL: https://github.com/apache/flink/pull/6781#discussion_r221640962
##
File path:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
##
@@ -74,6 +77,36 @@
}
}
+ /**
+* Verifies if the provided pattern can possibly generate empty match.
Example of patterns that can possibly
+* generate empty matches are: A*, A?, A* B? etc.
+*
+* @param pattern pattern to check
+* @return true if empty match could potentially match the pattern,
false otherwise
+*/
+ public static boolean canProduceEmptyMatches(final Pattern
pattern) {
+ NFAFactoryCompiler compiler = new
NFAFactoryCompiler<>(checkNotNull(pattern));
+ compiler.compileFactory();
+ State startState =
compiler.getStates().stream().filter(State::isStart).findFirst().get();
Review comment:
Ok, will change it. In general though I am always torn in this situations,
cause that would mean we have a bug in our compiler.
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[GitHub] dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method to check if pattern can produce empty matches
dawidwys commented on a change in pull request #6781: [FLINK-10470] Add method
to check if pattern can produce empty matches
URL: https://github.com/apache/flink/pull/6781#discussion_r221640962
##
File path:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
##
@@ -74,6 +77,36 @@
}
}
+ /**
+* Verifies if the provided pattern can possibly generate empty match.
Example of patterns that can possibly
+* generate empty matches are: A*, A?, A* B? etc.
+*
+* @param pattern pattern to check
+* @return true if empty match could potentially match the pattern,
false otherwise
+*/
+ public static boolean canProduceEmptyMatches(final Pattern
pattern) {
+ NFAFactoryCompiler compiler = new
NFAFactoryCompiler<>(checkNotNull(pattern));
+ compiler.compileFactory();
+ State startState =
compiler.getStates().stream().filter(State::isStart).findFirst().get();
Review comment:
Ok, will change it. In general though I am always torn in this situations,
cause that would mean we have a bug in our compiler, so it is actually not an
`IllegalState`
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