Class MarkLookBehindEntriesVisitor

java.lang.Object
com.oracle.truffle.regex.tregex.parser.ast.visitors.NFATraversalRegexASTVisitor
com.oracle.truffle.regex.tregex.parser.ast.visitors.MarkLookBehindEntriesVisitor
public class MarkLookBehindEntriesVisitor extends NFATraversalRegexASTVisitor
For all lookbehind assertions, mark all states where the assertion may begin. If an assertion may begin before the root of the AST, the AST is wrapped into a non-capturing group and prepended with a sequence of optional and non-optional any-char matchers, as shown in the following example: /(?<=ab)/ is transformed to /(?:[_any_][_any_](?:|[_any_](?:|[_any_])))(?<=ab)/. The sequence of non-optional any-char matchers is called "prefix", and is necessary for cases where we want to start searching for a regex match on a random position in a string. When starting on any other index than 0, we decrease the index by the length of the prefix (but stop at position 0) and thereby guarantee that lookbehind matches are found, but no regex match prior to the actual starting index is found. When starting at index 0, the prefix is ignored. When starting at index 1, just the last element of the prefix is used, and so on.

This entire mechanism assumes that all lookbehind assertion have a fixed length!

See Also: