12.8 Summary
Closures in Rust are pivotal for succinct, flexible, and safe code. They capture variables from their environment automatically, sparing you from manually passing extra parameters. The traits Fn, FnMut, and FnOnce reflect different ways closures handle captured variables—by immutable reference, mutable reference, or by taking ownership.
Rust’s move keyword ensures data is transferred into a closure if that closure outlives its original scope (for instance, in a new thread). You can store closures in variables, pass them to functions, and even return them. Thanks to Rust’s zero-cost abstractions, closures are typically as efficient as regular functions.
For C programmers accustomed to function pointers plus a void* context, Rust closures offer a more ergonomic and type-safe alternative. They are everywhere in Rust, from simple iterator adapters and sort keys to complex async and concurrent systems.
Overall, closures help make Rust code more expressive, while preserving the strong safety and performance guarantees that Rust is known for.