将对象实例转换为另一个实例的引用？

Question

In my framework I have a DataSource1 instance that was dropped in design time on a Form.
At some point at run time I need to "convert" it to a reference to another DataSource2 (on a Data Module).

Is simply setting:

DataSource1 := DataSource2;

Enough to make DataSource1 a reference of DataSource2? it appears that DataSource1 is not being destroyed at this point - It is destroyed when the Owner of DataSource2 is destroyed, And that there are in fact two instances of TDataSource.

Or do I need to explicitly free DataSource1 first?

DataSource1.Free;
DataSource1 := DataSource2;

What is the correct way? (Besides declaring DataSource1 as a reference in the first place)

Answer 1

When you declare a variable to be of a type that inherits from TObject, you are actually declaring a pointer.

When you call a constructor, you are creating an instance. The constructor returns a pointer to that instance. You typically assign that pointer to a variable like this:

Obj1 := TMyClass.Create;

You can make a second variable point to, or refer to, the instance with simple assignment:

Obj2 := Obj1;

The object is destroyed by calling Free:

Obj1.Free;

At this point Obj2 refers to an object that no longer exists. We say that Obj2 is a stale reference.

In your case you need to free the first object: