Tutorial: Understanding Identifier Scope and Namespaces

The identifier scope defines the locations where identifiers are visible in Shui documents. Identifiers may reference

• elements,
• element properties, events, and methods,
• modules (by alias).

Identifier Lookup Strategy

Looking for an identifier when resolving a reference starts in the element where the reference occured and follows this strategy:

• If the identifier is self, that element is returned.
• Otherwise, if the element has a member (property, method, event) with that identifier, that member is returned.
• Otherwise, if the identifier is this<Type>, and the element is of type <Type>, that element is returned.
• Otherwise, the children and descendents of the element are searched for an element with the identifier inside the local namespace (see below). If such an element exists, it is returned.
• Otherwise, the parent element is searched for the identifier in the same way (all the way going up to the root element, if necessary).
• If there was still nothing found, the list of loaded modules is searched for a module with that name.
• If the search did not turn up anything, undefined is returned.

All locations thus searchable specify the identifier scope.

Advanced: The function __rslv__ is Shui's resolver function implementing the lookup strategy. It takes the identifier as a string value and has everything else it needs in its function closure.

Identifier Namespaces

The same element may hold different identifiers in different namespaces. For instance, when creating a component file, the identifiers used inside the file are not visible outside and the identifier of the root element may differ.

// MyComponent.shui

Box {
    id: daBox

    Label {
        id: boxLabel
        text: "In da box"
    }
}

// main.shui

require "./MyComponent.shui";

Document {

    MyComponent {
        id: myBox

        Label {
            // THIS DOES NOT WORK: boxLabel is a sibling of this label, but
            // its identifier is not known in the local namespace
            //text: "Boxed: " + boxLabel.text
        }
    }

}

Note how MyComponent has the identifier daBox in MyComponent.shui, but is known by myBox in main.shui. This is the same element instance, known by different identifiers in different namespaces.

Note also how boxLabel from MyComponent.shui is not known in the local namespace of main.shui, even though it is a descendent element.

Namespaces are assigned automatically by the Shui compiler (see fengshui) at compile time and may be accessed by the __namespace constant as a string value.

All Shui files and also templates get their own namespace this way.