hphp/hack/manual/apis/Classes/HH.Readonly/Shapes/idx.md
:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::
Use Readonly\Shapes::idx to retrieve a field value in a shape, when the key may or may not exist
public static function idx(
shape(...) $shape,
arraykey $index,
mixed $default = NULL,
): mixed;
If $index does not exist in the shape, the default value will be returned ($default), if one has been set.
It behaves similarily to idx() for Collections.
A few examples:
Shapes::idx(shape('x'=> 123), 'x') // 123
Shapes::idx(shape('x'=> 123), 'y') // null
Shapes::idx(shape('x'=> 123), 'y', 456) // 456
Shapes::idx(null,'y', 456) // 456
Use Shapes::idx when the key in your shape is optional (e.g., ?x, in shape(?'x' => int).
If the key in your shape is always present, access the value directly: $my_shape['x'].
The second argument, $index must always be a literal.
shape(...) $shape - shape to search for $index.arraykey $index - Key ($index) to search. Must be a literal!mixed $default = NULL - Default value to return if $index does not exist. By default, returns null.$value - - Value at $index, if it exists, or $default.