Objects and Interfaces

BrightScript Objects

Though BrightScript operates independently of its object architecture and library, they are both required for programming BrightScript applications. The API of a BrightSign platform is exposed to BrightScript as a library objects: Platforms must register a new BrightScript object to expose some part of its API.

BrightScript objects are written in C (or a compatible language such as C++), and are robust against version changes: Scripts are generally backwards compatible with objects that have undergone revisions. 

BrightScript objects keep a reference count; they delete themselves when the reference count reaches zero.

Wrapper Objects

All intrinsic BrightScript types (Boolean, Integer, Float, Double, String, and Invalid) have object equivalents. If one of these intrinsic types is passed to a function that expects an object, the appropriate wrapper object will be created, assigned the correct value, and passed to the function (this is sometimes referred to as "autoboxing"): This allows, for example, roArray objects to store values (e.g. integers and strings) as well as objects.

Any expression that expects one of the above types will work with the corresponding wrapper object as well: roBoolean, roInt, roFloat, roDouble, roString.

The following examples illustrate how wrapper objects work:

Interfaces

Interfaces in BrightScript operate similarly to Java or Microsoft COM: An interface is a known set of member functions that implement a set of logic. In some ways, an interface is similar to a virtual base class in C++; any script or program that is compatible with C can use an object interface without regards to the type of object it belongs to: For example, the roSerialPort object, which controls the standard serial interface, implements three interfaces: ifSerialControl, ifStreamReceive, and ifStreamSend. Since the print statement sends its output to any object that has an ifStreamSend interface, it works with the roSerialPort object, as well as any other object with the ifStreamSend interface.

Statement and Interface Integration

Some BrightScript statements have integrated functionality with interfaces. This section describes how to use statements with interfaces.

PRINT

Using the PRINT statement in the following format will print into an object that has an ifStreamSend interface, including the roTextField and roSerialPort objects:

If the expression being printed evaluates to an object with an ifEnum interface, the PRINT statement will print every item that can be enumerated.

In addition to printing the values of intrinsic types, the PRINT statement can also be used to print any object that exposes one of the following interfaces: ifString, ifInt, ifFloat.

WAIT

The WAIT statement can work in conjunction with any object that has an ifMessagePort interface.

Expression Parsing

Any expression that expects a certain type of variable—including Integer, Float, Double, Boolean, or String—can accept an object with an interface equivalent of that type: ifInt, ifFloat, ifDouble, ifBoolean, ifString.

Array Operator

The [ ] array operator works with any object that has an ifArray or ifAssociativeArray interface, including arrays, associative arrays, and lists.

Member Access Operator

The member access operator (i.e. Dot Operator) works with any object that has an ifAssociativeArray interface. It also works with any object when used to call a member function (i.e. method). It also has special meaning when used on an roXMLElement or roXMLList object.