protected function prepare()
    {
        $symbolRegistry = new SymbolRegistry();
        $symbolClassesNames = $symbolRegistry->getSymbols();

        foreach ($symbolClassesNames as $symbolClassName) {
            /** @var AbstractSymbol $symbol */
            $symbol = new $symbolClassName($this->stringHelper);

            // Notice: We cannot use add() here, because validation might fail
            // if we do not add the Numbers class as the first symbol.
            $this->symbols[$symbolClassName] = $symbol;
        }

        $this->validate();
    }