pnowojski 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_r222622968
##########
File path:
flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/compiler/NFACompiler.java
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@@ -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:
But that's the convention: you `checkState`, `checkArgument`, throw
`IllegalStateException` or `IllegalArgumentException` to cover for bugs in the
code - the situations/class states that should never happen.
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