operator[] is implemented in class SymbolContainer. Its functionally is the same as in std::vector, it returns a Symbol only if its associated key already exists in the container; otherwise it is undefined behavior (meaning it can't be used to add new elements, use emplace and insert instead).
Bug fixes:
Parser class throw UnusedSymbol exception, as expected, if Expression instances are created specifying variables which tokens don't exist in the expression in from_infix and from_postfix methods.
New features:
operator[]is implemented in classSymbolContainer. Its functionally is the same as instd::vector, it returns aSymbolonly if its associated key already exists in the container; otherwise it is undefined behavior (meaning it can't be used to add new elements, useemplaceandinsertinstead).Bug fixes:
Parserclass throwUnusedSymbolexception, as expected, ifExpressioninstances are created specifying variables which tokens don't exist in the expression infrom_infixandfrom_postfixmethods.