How to structure an anchor program?

Question

I see that most programs put everything in a lib.rs file. My file is more than 500 lines so I feel like it should be multiple files.

I have seen people using a file error.rs for errors so I have done that.

Is there guidelines or good practices to continue splitting my big program ?

Answer 1

Bigger projects typically use the multiple files template added in Anchor 0.29. You can do this for new projects with:

anchor init counter --template=multiple

This splits up state/ and instructions/. Under these folders, you can create files for each account type and instruction handler.

For example, a simple counter program might look like:

src/
  instructions/
    decrement.rs
    increment.rs
    initialize.rs
    mod.rs
  state/
    counter.rs
    mod.rs
  lib.rs
  errors.rs
Cargo.toml
README.md

Answer 2

A single lib.rs file can be good enough, even for 500-line code. There are some Solana programs with thousands of lines that use this format. It is very debatable which method is considered best though. It all depends on preference.