Essential Keywords Reference
What you’ll learn: A compact keyword map for Java developers so Rust syntax stops looking alien during the first few chapters.
Difficulty: 🟢 Beginner
This chapter is a quick reference, not a replacement for the conceptual chapters.
| Rust keyword | Rough Java analogy | What it usually means |
|---|---|---|
let | local variable declaration | bind a value to a name |
mut | mutable local variable | allow reassignment or mutation |
fn | method or function declaration | define a function |
struct | class or record shell | define a data type with fields |
enum | enum plus sealed hierarchy | tagged union with variants |
impl | method block | attach methods or trait impls |
trait | interface | shared behavior contract |
match | switch expression | exhaustive pattern matching |
if let | guarded destructuring | handle one successful pattern |
while let | loop while match succeeds | consume values until pattern stops matching |
pub | public visibility | expose outside the module |
crate | module or artifact root | current package boundary |
use | import | bring names into scope |
mod | package or nested module | declare a module |
ref | bind by reference in a pattern | avoid moving during pattern matching |
move | capture by value | transfer ownership into closure or thread |
async | async method marker | function returns a future |
await | future completion point | suspend until result is ready |
unsafe | dangerous low-level block | programmer must uphold invariants |
where | generic bounds clause | move trait bounds out of the angle brackets |
Self | current class type | current implementing type |
dyn | interface reference | dynamic dispatch through a trait object |
const | compile-time constant | inlined immutable value |
static | static field | process-wide storage |
Three Keywords That Need Extra Attention
mut
Mutability is explicit on the binding:
#![allow(unused)]
fn main() {
let x = 1;
let mut y = 2;
y += 1;
}match
match is not just a switch statement. It is a pattern-matching expression and must usually cover every case.
move
Java developers often underestimate move. In Rust it matters whenever values enter closures, threads, or async tasks.
Keep this table nearby during the first pass through the book. After a few chapters, most of these keywords become second nature.