for / in

for iterates over the elements of a collection or the values of a range, binding each in turn to the loop variable.

for item in collection {
    Print(item);
}

Iterating a Collection

A for loop walks a slice element by element, in order. The loop variable holds each element directly — no index bookkeeping is required:

let nums = [1, 2, 3, 4, 5];
var sum = 0;
for n in nums {
    sum += n;
}

Iterating a Range

A range generates a sequence of integers. 0..10 is half-open — the end is excluded — while 0..=10 includes the end:

for i in 0..10 {
    Print(i);   // prints 0 through 9
}

for i in 0..=10 {
    Print(i);   // prints 0 through 10 (inclusive)
}

Ranges are the idiomatic way to repeat something a fixed number of times or to walk a collection by index when you need the position.

Exiting Early

break leaves the loop immediately; continue skips to the next element or value.

See Also

• while — looping on a condition rather than a sequence
• Slices — the collections for iterates over
• break / continue — altering loop control flow