How best to add Plugin Capability to a Delphi program

Question

I am looking to add the capability for users to write plugins to the program I have developed in Delphi. The program is a single executable with no DLLs used.

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Answer 1

I tried to make an overview of all such options some time ago. Together with my readers/commenters we built this list:

• DLL/BPL loaded from the program.
• DLL/BPL loaded from a sandbox (which could be another copy of the program or a specialized "server" application and which communicates with the main program via messages/sockets/msmq/named pipes/mailslots/memory mapped files).
• COM (in any of its variants).
• DDE (please not).
• External program that communicates via stanard input/output.
• External program that communicates via files (file name is a parameter to the program).
• External program that works via drop folder (useful for batch processing).
• External program that communicates with windows messages/windows sockets/msmq/named pipes/mailslots/memory mapped files/database publish-subscribe.