Semicolons
Q: What do semicolons do in Rust?
A: Think of it this way: Rust forces you to pick a side. Are you producing a value, or are you just doing something?
Q: So an expression produces a value, like 1 + 2 → 3?
A: Exactly. A statement is the opposite—it’s an action with no return value. let x = 5; or println!() don’t yield anything useful, they just do.
Q: And blocks like { 1 + 2 }?
A: That’s an expression. The block evaluates to whatever its last line evaluates to. { let x = 5; x + 1 } → 6.
Q: So what happens if I slap a semicolon on the end: { let x = 5; x + 1; }?
A: You just killed it. The semicolon discards the value. It converts an expression into a statement. No return, no value, nothing to pass back.
Q: So semicolons are basically Rust’s way of saying: “shut up, I don’t care about your result.”
A: That’s it. And this matters, because Rust won’t let you be vague. A function must either return something or not—no half-measures. That’s why you drop the semicolon in function bodies, async blocks, and match arms when you do want the value to flow out.