Recipe

Translate a function into Rust

Use when: you're porting a function from C++, C#, Java, Python, JavaScript or Go and want Rust that compiles and reads as Rust

Goal: a Rust function whose signature says who owns each value, what can be missing and what can fail

Taught in The translation table

1. 1

   For each parameter: only reads it, changes it, or keeps it.

   • only reads — &T, &str or &[T].
   • changes it — &mut T.
   • keeps it (stores or returns it) — an owned T.

   Why: this is the one decision the source language made for you, and every borrow error later traces back to it.

2. 2

   Every null, None, nil or "not found" result the function can produce becomes Option<T>.

   Example

   Python's return None when a key is absent becomes -> Option<f64>, with None in that branch and Some(avg) in the other.

   Why: the caller is then forced to handle the empty case instead of discovering it at run time.

3. 3

   Every throw, raise or returned error becomes an Err in a Result<T, E>, and each call that can fail gets a ?.

   Why: failures become part of the signature, and ? marks each place one leaves the function.

4. 4

   Classes become structs with impl blocks, closed sets of kinds become enums, and interfaces become traits.

   Why: these are the rows of the table that change the design rather than the syntax, so settle them before the body.

5. 5

   Translate the body using the table's "new spelling" rows, compile, and fix what the compiler reports.

   Why: the compiler checks the ownership choices from step 1 against how the body really uses each value.