Assignment and Indexing

Assignment is an expression. It stores a value and returns that value:

$target = 0;
$result = ($target = 5);

assert!($target == 5);
assert!($result == 5);

Targets

An assignment target may be:

a variable;
an object property;
a static property;
a vec or dict index;
a vec append target, $values[];
a tuple or dict destructuring pattern.

Literals, arithmetic results, strings, and tuple entries are not writable targets. A property on an object returned by a call is writable because the object keeps its identity.

Compound assignment

Whim supports these compound forms:

+=  -=  *=  /=  %=  **=  .=
&=  |=  ^=  <<=  >>=  &&=  ||=  ??=

The target expression runs once:

final class Counter {
  public int $calls = 0;

  public function index(): int {
    $this->calls++;
    return 0;
  }
}

$counter = new Counter();
$values = vec[10];
$values[$counter->index()] += 1;

assert!($counter->calls == 1);
assert!($values[0] == 11);

&&=, ||=, and ??= short-circuit like their non-assignment forms.

Tuple and vec destructuring

A tuple target accepts a tuple or vec:

($name, $age) = ('Ada', 36);
assert!($name == 'Ada');
assert!($age == 36);

Without a rest target, the source size must match. A trailing rest target collects the remaining values in a vec:

($head, ...$tail) = vec[1, 2, 3];
assert!($head == 1);
assert!($tail == vec[2, 3]);

Use bare ... to allow and ignore the rest.

Defaulted targets

A default runs only when its position is missing. A present null does not use the default:

($name, $role = 'member') = vec['Ada'];
assert!($role == 'member');

($id, $label = 'fallback') = vec[1, null];
assert!($label == null);

A default may use an earlier binding. Once one target has a default, every later fixed target must also have one. A rest target may follow them.

Dict destructuring

A dict target selects named keys:

$source = dict['id' => 7, 'profile' => dict['name' => 'Ada']];
dict['id' => $id, 'profile' => dict['name' => $name]] = $source;

assert!(($id, $name) == (7, 'Ada'));

Each key expression runs before the source expression. A missing key throws. The source must be a dict.

Write order

Whim reads the full source before it writes any target. A target may reuse the source variable without changing later reads:

$values = (1, 2, 3);
($values, $second, $third) = $values;
assert!(($values, $second, $third) == (1, 2, 3));

Whim writes targets from left to right. If one variable appears twice, the last write wins. $_ follows the same rule because it is an ordinary variable.

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