Classes
Contents
- Introduction
- Basic Notation
- Structure vs Data
- Prototypes
- Static Structure
- Pointer to a Class
- Object Reference with a Class
- Object Reference without a Class
- Conclusion
Introduction
The contents of an object can be arbitrary. Anything can be put inside an object:
But an object can also select another object to serve as its class or prototype.
That class determines what type of object it is. A class can be thought of as a special object, a sort of blue-print, that aims to describe characteristics and behavior for other objects.
Basic Notation
The basic notation in Circular for pointing out a class is as follows:
The object on the left points out the class on the right.
A dashed line between the circles means that it points out a class:
A line dissector can indicate direction, sort of like an arrow head:
The class can be drawn out as a dashed circle to make it extra clear it functions as a class:
Structure vs Data
When an object has a class, the contents of that object might not be so arbitrary anymore:
An object initially shows contents identical to the class. An object might have the same structure as its class, but can have data that may change freely:
While the structure of the object is still the same, the data appears to have changed. Values may freely change as well as which related objects it points to.
Prototypes
An alternative notation is a class drawn with a solid line shape instead:
Using shapes with dashed lines is sort of optional.
This solid line shape notation, might also be used for a distinction between classes and prototypes: where an object is initially a copy of another object, but anything may be changed about it, even its structure.
Static Structure
To visually distinguish static structure from object structure, other parts of the static (or class) structure could be drawn with dashed lines too:
The rules are not that precise when it comes to shapes drawn with different line styles.
Pointer to a Class
A class can be referenced like an object, using an object line. This establishes an pointer to a class:
That solid line in the middle means it is a pointer.
Perhaps it would look neater if the pointer is drawn with a dashed shape too:
In .NET and C# these pointers to classes might represent Type objects and type arguments.
Object Reference with a Class
Just like an object, an object reference can have a class as well. In that case merely objects of that class can be referenced:
The object reference points out Class A. The object also points out Class A. The solid line between object and object reference is valid, because they both have the same class.
Now the object reference still points out Class A. But the object points out Class B instead. The solid line between shapes is not valid anymore, because they have different types.
Object Reference without a Class
For an object reference that does not have a class, any object can be pointed at:
The object reference does not point out a class. Therefore it can point at an object of any class. It points at an object, which so happens to be of Class A.
Here the object points out Class B instead of Class A. But since the object reference does not have a class, it can point to objects of Class B too.
Conclusion
Hopefully this gave an impression of how class notation looks in the Circular language. Dashes seem to be key in its notation.