Should requests for code that implement some method relevant to the field be considered on-topic? An answer to such a question could consist of just the (pseudo)-code or a link to a full implementation.
Of course it's on topic. Why not? As long as it's about quantitative finance and not too basic like asking how to discount a single cashflow. Sharing source code will help everybody.
It depends how it's asked obviously.
If the question shows enough effort was done and points out to a specific problem, then yes.
If the question is blunt and just asks for the code, then no.
I think a question about best implementations of different methods (like "which library is recommended for XXX") is fine as well.