But also in the real world I may not be interested in any error information for the library I’m using. I’d like to be able to pass a null for the error information structure and have the compile optimize away everything related to tracking and storing error information.

I’d like my parser library to be able to give me the exact file, line and column number an error occurred. But I’d also like to use the library in a “just give me an error if something failed, I don’t really care why” mode.