Expressions And Operators: Subscript

The subscript operator, [...] is used to designate an element of a string, a vec, a dict, or a keyset. The element key is designated by the expression contained inside the brackets. For a string or vec, the key must have type int, while dict and keyset also allow string. The type and value of the result is the type and value of the designated element. For example:

$text = "Hello";
$e = $text[4];    // designates the element with key 4 value "o"
$text[1] = "?";   // changes the element with key 1 from "e" to "?"

$v = vec[10, 25, -6];
$e = $v[1];     // designates the element with key 1 value 25
$v[2] = 44;     // changes the element with key 2 from -6 to 44

$d = dict["red" => 4, "white" =>12, "blue" => 3];
$e = $d["white"]; // designates the element with key "white" value 12
$d["red"] = 9;    // changes the element with key "red" from 4 to 9

For a vec, the brackets can be empty, provided the subscript expression is the destination of an assignment. This results in a new element being inserted at the right-hand end. The type and value of the result is the type and value of the new element. For example:

$v = vec[10, 25, -6];
$v[] = 99;    // creates new element with key 3, value 99