A data race that doesn’t compile

▤ Summary

The article explains how a Rust-based learning library uses the type system to prevent parallel reducer data races at compile time. It starts with a failed attempt to prove that reducer slices are all distinct, then reframes the problem as a compile-time matching problem. The solution uses heterogeneous lists, recursive trait resolution, and position witnesses to let the compiler verify a one-to-one mapping between state slices and reducers. When the mapping is wrong, the build fails before runtime, which turns a concurrency risk into a compile-time guarantee. The result improves performance by parallelizing independent reducers while preserving deterministic behavior.

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