Objectives
Build a consumer that calls a binary NIF, a resource, and a dirty scheduler, and describe Rustler and Zigler without claiming their safety proofs.
Why
The point of the library is that an Elixir app can do those three things without writing ErlNifEntry. The point of the comparison is to see which guarantees come from a type system we did not run.
Model
Rustler Rust crate, rustc, Rust ownership, NIF macros. Not compiled here.
Zigler Zig, comptime, `zig` toolchain. Not compiled here.
Mojoler Mojo 1.1.0, generated ABI, JSON declarations, measured on this OTP.Theory
Rustler's public docs (https://github.com/rusterlium/rustler and the Hex docs at https://hexdocs.pm/rustler) describe deriving NIF wrappers from Rust functions and using Rust's borrow checker on the native side. Zigler's docs (https://github.com/e-xyza/zigler) describe Zig types and comptime checks against the NIF API. This checkout did not clone either project and did not record their versions. Their ergonomic goal — declare a function, get a stub and a safe wrapper — is the same goal as tools/dsl/decls.json. The implementation is not the same, and Mojo 1.1.0's origins did not accept every pointer we wanted to write through. Where the compiler could not enforce a lifetime, the code uses a runtime error (:not_binary, :borrowed, :frozen) or refuses the declaration.
Measured Mojoler properties are the ledger, not the resemblance to Rust.
Lab
cd examples/consumer && mix test
mix test test/dsl_test.exs test/own_test.exs test/sched_test.exs
From the repo root for the second command.
Expected
The consumer prints a pass for add(20, 22). The second command covers shift (copy), borrow_len (strict failure on a list), Box.bump (resource), and the dirty heartbeat.
Code
examples/consumer/lib/consumer.ex calls Mojoler.POC.add/2. The resource and the scheduler are in the main app's tests because the consumer fixture is the packaging proof, not a second copy of every example. A reader adding a function follows unit 15: a JSON object, a user .mojo file, generate.py, mix test.
Failure
Writing the entry struct in the user file. native/examples/arith_user.mojo has no ErlNifEntry. If a new example grows one, it has left the DSL.
Exercise
Name one guarantee Rust's borrow checker is documented to provide that this Mojo code checks only at runtime.
Answer
Aliasing. Freeze rejects an outstanding borrow by reading a counter under a mutex (:borrowed). That is a dynamic check. It is not a compile error in the caller's Elixir, and it is not the Rust rule that a mutable reference excludes other references. The generator does reject a borrow combined with a dirty schedule before compile of that bad file, which is a static check of a declaration, not of arbitrary Mojo.