Yesterday when I was thinking about that enumerators I had an idea for a
language feature and something which I saw introduced in Objective-C some years
ago.
Retaining of a member variable through a property is a common pattern I do
everyday nearly. In my root class I manage a simply retain count which frees
the object when it reaches 0. When assigning variables that the receiver wants
to take ownership of on assignment I have to make an accessor which manages the
retain count of the object (boring boiler plate).
Consider the example below where the root class (TObject) overrides a class
function which performs this retain count management (ManageObject). In the
other class there is a member of type TObject which TMyClass will take
ownership of when assigned. If the property “Data” includes the “managed”
keyword the compiler will automatically call ClassType.ManageObject() and take
the return value as the variable which is written to “m_data”.
I’ve been wanting to learn how to contribute to the compiler for years now but
maybe this is an easy enough project to start with. I don’t know if this is a
problem people have though but I assume it may be since Objective-C had a
system like for memory management and properties. What do you think? How do
most FPC programmers handle memory these days?
type
TObject = class
class function ManageObject (obj: pointer): TObject; override;
end;
type
TMyClass = class (TObject)
private
m_data: TObject;
public
property Data: TObject read m_data write m_data;
managed;
// if there’s a write method defined the compiler calls
ManageObject before the write method
property MyData: TObject read m_data write SetData;
managed;
end;
class function TObject.ManageObject (obj: pointer): TObject; override;
begin
if obj <> nil then
result := TObject(obj).Retain;
else
begin
TObject(obj).Release;
result := nil;
end;
end;
Regards,
Ryan Joseph
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