if / else

The if statement lets your program make decisions based on conditions.

Basic if

if count > 3 {
  print("That's a lot!")
}

The condition does not need parentheses, but they’re allowed: if (x > 3) { ... }. Braces are always required.

if / else

if temperature > 30 {
  print("It's hot!")
} else {
  print("Not too bad.")
}

if / else if / else

Chain multiple conditions with else if:

if score > 90 {
  print("Excellent!")
} else if score > 70 {
  print("Good job!")
} else if score > 50 {
  print("Not bad!")
} else {
  print("Keep trying!")
}

Only the first matching branch runs. If none match and there’s an else, that branch runs.

if as an expression

if/else can produce a value when used in expression position (e.g., after =):

let label = if count > 3 { "lots" } else { "few" }
print("You have {label} of items")

When used as an expression, both if and else branches are required. The last expression in each branch is the value.

let message = if x > 0 {
  "positive"
} else {
  "non-positive"
}
print(message)

Common patterns

Guard clause

fn process(value) {
  if value == none {
    return
  }
  print("Processing: " + str(value))
}

Classify a value

fn classify(n) {
  if n > 0 {
    return "positive"
  } else if n < 0 {
    return "negative"
  } else {
    return "zero"
  }
}

Combine conditions with && and ||

if age >= 18 && has_ticket {
  print("Welcome in!")
}

if x < 0 || x > 100 {
  print("Out of range!")
}