An object handle is a type that can hold a reference to an object. With object handles it is possible to declare more than one variables that refer to the same physical object.
Not all types allow object handles to be used. None of the primitive data types, bool, int, float, etc, can have object handles. Object types registered by the application may or may not allow object handles, verify the applications documentation.
An object handle is declared by appending the @ symbol to the data type.
object@ obj_h;
This code declares the object handle obj and initializes it to null, i.e. it doesn't hold a reference to any object.
In expressions variables declared as object handles are used the exact same way as normal objects. But you should be aware that object handles are not guaranteed to actually reference an object, and if you try to access the contents of an object in a handle that is null an exception will be raised.
object obj; object@ obj_h; obj.Method(); obj_h.Method();
Operators like =, or any other operator registered for the object type work on the actual object that the handle references. These will also throw an exception if the handle is empty.
object obj; object@ obj_h; obj_h = obj;
When you need to make an operation on the actual handle, you should prepend the expression with the @ symbol. Setting the object handle to point to an object is for example done like this:
object obj; object@ obj_h; @obj_h = @obj;
An object handle can be compared against another object handle (of the same type) to verify if they are pointing to the same object or not. It can also be compared against null, which is a special keyword that represents an empty handle.
object@ obj_a, obj_b; if( @obj_a == @obj_b ) {} if( @obj_a == null ) {}
An object's life time is normally for the duration of the scope the variable was declared in. But if a handle outside the scope is set to reference the object, the object will live on until all object handles are released.
object@ obj_h; { object obj; @obj_h = @obj; // The object would normally die when the block ends, // but the handle is still holding a reference to it } // The object still lives on in obj_h ... obj_h.Method(); // ... until the reference is explicitly released // or the object handle goes out of scope @obj_h = null;