I’ve been wrapping a few tool types in a Rust project lately and ran into some friction. Along the way I picked up a few practical lessons on what a clean tool type should look like. Here’s what I landed on:
Decouple unrelated fields:
The first and hardest step is deciding which fields the type actually owns. Real-world code is full of types that do more than they should; those extra responsibilities are usually candidates for being pulled out.
Prefer immutable interfaces:
A good tool type should expose only immutable methods so callers never need a mutable handle. Rust’s type system pushes you in this direction, and following it let me drop a lot of interior-mutability wrappers I had previously needed at runtime.
Distinguish different kinds of output:
Some values are fixed once the type is created; others change over time. The former can stay as plain owned types, while the latter are better expressed as shared types. I also try to avoid handing out mutable references. When mutation is required, specific methods should own that responsibility.
Insight:
A surprising amount of this is already enforced by the Rust type system. The rules can feel strict, but treating the compiler as a collaborator usually leads to cleaner design and less code.
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