Attribute grammars: How are attributes implemented?
Attribute grammars are a conceptual tool. You are mixing this up with implementation details.

There are many parser generators around (check for example the Wikipedia pages on compiler compilers and comparison of parser generators). They all implement some flavor of attribute grammar, in actual use you aren't interested in a parse tree or a derivation. The most used ones are (direct descendants of) old designs, which predate the current object oriented craze, and write parsers  implemented in languages like C, with no objects.