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AN672

PRECISION32™ SI32LIBRARY OVERVIEW

Silicon Laboratories 

AN672

6. Object Component

COMPONENT: si32ObjectComponent

REQUIRES: si32BaseComponent

PROVIDES: si32RootObject

Although it is sometimes practical to implement applications in C++ by using only a subset of the language’s

features, use of C++ may be precluded by the target application's requirements. The si32Library object system

provides a C99 based subset of the capabilities of C++ for use in applications where C++ is inappropriate or

unavailable. The si32Library is object based, providing encapsulation, inheritance, and polymorphism. The object

system provides a simple class hierarchy, but is neither truly class or prototype based. It is simply a design pattern

that uses structure composition and aggregation to implement a type system wherein new types can be derived

from base types, inheriting their behavior and properties. Therefore, the term class is generally avoided.

In many cases the precise type of an object is known a-priori, at compile time. In such cases, early binding can be

employed effectively to eliminate indirect function calls. For example:

_SomeType_SomeOperation(SomeObject, SomeArguments);

In other cases, however, late binding is necessary because the type of an object is not known until run-time. This is

particularly true for objects representing optional hardware that is discovered at run-time. For example:

SomeObject->Operations->SomeOperation(SomeObject, SomeArguments);

The si32ObjectComponent provides both early and late binding capabilities.

Objects are implemented as C structures. These structures contain specific fields and are constructed in a manner

that facilitates the implementation of inheritance by means of structure composition. Figure 4 shows the essential

structure of a base object.

obj* my_ object

functions

variable

...

variable

(*fn)()

...

(*fn)()

Figure 4. Object Structure

An object's variables can be accessed in this manner:

my_object->context.variable

The object’s functions can be called as follows:

my_object->context.functions->fn(my_object, ...)

An object reference (or a pointer to an object) is represented by the type obj*. This is an anonymous (void) pointer

that can reference anything. Therefore, it must be assigned to a variable of the appropriate type and checked at

runtime.

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Rev. 0.1

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