Control Flow

Shape is expression-oriented.

If Expressions

let score = 84

let grade = if score >= 90 {
  "A"
} else if score >= 80 {
  "B"
} else {
  "C"
}

print(grade)

Blocks Return Values

The last expression in a block is the value.

let value = {
  let base = 10
  base * 2
}

print(value) // 20

A trailing semicolon discards the value and yields ().

let unit = {
  1;
}

For Loops

for i in 0..5 {
  print(i)
}

Destructuring works in loop bindings:

let points = [{x: 1, y: 2}, {x: 3, y: 4}]

for {x, y} in points {
  print(f"({x}, {y})")
}

While Loops

let i = 0

while i < 3 {
  print(i)
  i = i + 1
}

Break and Continue

for i in 0..10 {
  if i == 2 {
    continue
  }
  if i == 6 {
    break
  }
  print(i)
}

Loop

loop creates an infinite loop. Use break to exit:

var i = 0
loop {
    if i >= 5 {
        break
    }
    print(i)
    i = i + 1
}

Break with Value

break can carry a value, making loop an expression. The value passed to break becomes the result of the loop block:

let result = loop {
    let x = compute()
    if x > 10 {
        break x * 2
    }
}
// result is the first x * 2 where x > 10

This pattern is useful when a value must be computed iteratively and the number of iterations is not known in advance.

Match

match is also an expression. See Pattern Matching.