A predeclared class in VBA and a static class (as found in languages like C#) are not the same concept, although they share some functional similarities in how they can be accessed.
Predeclared Class in VBA:
- In VBA, a class module can be set with the VB_PredeclaredID attribute set to True. This creates a default instance of the class that is automatically available and can be accessed directly using the class name, without needing to explicitly declare and create an object variable using New.
- This behavior is similar to how Form modules work in VBA, where you can refer to Form1.TextBox1.Text directly without explicitly creating an instance of Form1.
- While it provides a readily available instance, it's still an instance of the class, meaning it can hold state and you can create additional instances of the same class if needed.
Static Class (in other languages like C#):
- A static class, in languages that support it, is a class that cannot be instantiated. You cannot create objects of a static class using the new operator.
- All members (methods, properties, fields) within a static class must also be static.
- Static classes are typically used for utility functions or collections of related methods that do not require an object instance to operate and often do not maintain state specific to an instance.
Key Differences:
- Instantiation:
A predeclared class in VBA can be instantiated (you can create new instances), even though a default one is provided. A static class cannot be instantiated.
- State:
A predeclared class's default instance can hold state specific to that instance, and other instances can have their own state. A static class, by design, typically does not hold instance-specific state.
- Purpose:
Predeclared classes in VBA are primarily a convenience for accessing a single, default instance easily. Static classes are a design pattern for groups of related functionality that don't require object instantiation.
In summary, while both allow direct access without explicit object creation, a predeclared class in VBA provides a readily available instance of a class, whereas a static class represents a type that cannot be instantiated and contains only static members.