if as an Expression

Goal of This Episode

Learn to treat if as an “expression” and use it directly to assign a value to a variable.

Main Text

This is the last episode of Chapter 1! Today I’ll introduce one of Rust’s cool features — if isn’t just for making decisions; it can also return a value.

First, the Usual Way

Suppose you want to give a variable different values based on a condition. You might write:

fn main() {
    let condition = true;
    let x;

    if condition {
        x = 1;
    } else {
        x = 2;
    }

    println!("{}", x);
}

Nothing wrong with that — but Rust has a more concise way.

if as an Expression

fn main() {
    let condition = true;
    let x = if condition { 1 } else { 2 };

    println!("{}", x);
}

Running it prints 1.

See that? The whole if condition { 1 } else { 2 } sits on the right side of let x =, assigning its result directly to x.

If condition is true, x is 1; if it’s false, x is 2.

Note: No Semicolons Inside the Braces

fn main() {
    let condition = true;
    let x = if condition { 1 } else { 2 };
    //                      ^          ^
    //                no semicolon  no semicolon
}

Those values (1 and 2) have no semicolon after them. In Rust, a value without a semicolon is the “return value.” This is Rust’s expression syntax — we’ll go into more detail when we learn about functions.

Both Sides Must Have the Same Type!

fn main() {
    let condition = true;
    let x = if condition { 1 } else { "hello" }; // ❌ Error!
}

This fails, because 1 is an integer and "hello" is a string. Rust won’t allow x to be sometimes a number and sometimes a string — it needs one definite type.

The values inside the two sets of braces must have the same type:

fn main() {
    let condition = true;

    // ✅ Both sides are integers
    let x = if condition { 1 } else { 2 };

    // ✅ Both sides are strings
    let msg = if condition { "good" } else { "bad" };

    // ❌ One side an integer, the other a string
    let bad = if condition { 1 } else { "hello" };
}

What’s the Benefit?

1. x doesn’t need to be mut.
2. The code is more concise.
3. It reflects Rust’s design philosophy: many things are “expressions” that can return values.

Recap

• In Rust, if is an expression and can return a value directly: let x = if condition { 1 } else { 2 };.
• The part inside the braces that serves as the return value takes no semicolon.
• The if and else sides must have matching types.

Congratulations on finishing Chapter 1! 🎉 You’ve learned Rust’s basic syntax: variables, arithmetic, conditionals, loops, types, and more. In the next chapter, we’ll start learning more of Rust’s distinctive features!