foreach

foreach walks an array, mapping, string, or buffer. Prefer it over an indexed for when you do not need the index.

foreach (type variable in aggregate)
    statement;

The body may be a block. break and continue work as in for / while.

Arrays

string *names = ({ "ada", "bek", "cy" });

foreach (string name in names) {
    write(name + "\n");
}

Declare the loop variable in the foreach header, or reuse an existing local:

string name;
foreach (name in names)
    write(name + "\n");

Mappings

One variable receives values. Two variables receive key then value. The key must not be a ref.

mapping scores = ([ "ada": 10, "bek": 7 ]);

foreach (string name, int score in scores) {
    write(name + " => " + score + "\n");
}

foreach (int score in scores) {
    write(score + "\n");
}

Strings and buffers

A string iterates characters (codepoint-oriented; a multi-codepoint grapheme cluster can error if you treat it as a single indexed char — see ref). A buffer iterates bytes as int values 0–255.

foreach (int b in buf) {
    write(sprintf("%02x ", b));
}

Mutating in place (ref / &)

ref (or &) on the loop variable writes back into arrays, buffers, and mapping values. It does not rewrite the source string variable.

int *nums = ({ 1, 2, 3 });
foreach (int ref n in nums)
    n *= 2;
// nums is ({ 2, 4, 6 })

Details and restrictions: ref.

await inside foreach

An async function may await inside a foreach over a local aggregate. See async and the async concept guide.