Using a freepascal library (.dylib) from mono

Question

While learning C# and Delphi Prism for use with monotouch is rewarding, I am looking for a way to re-use code written in ordinary Object Pascal. To simply re-write everything I have done in Delphi over 15 years is simply unacceptable.

So my question is twofold:

1. If I for sake of argument have a library written in ordinary Object Pascal with no external dependencies and compiled with the ARM freepascal compiler for iPhone - could I use the resulting dylib from monotouch?
2. If the above is correct, how do I declare and call these external functions from C#/Prism? How do i deal with passing record types etc. in mono?

I have noticed that other iPhone applications ship with their own dylib files (the SDL game library is a typical example). I find no reason why this should not work.

Answer 1

I have not worked with monotouch, but Mono/.NET have a feature called P/Invoke (platform invoke).

Basically you declare your functions/procedures as extern in the managed code and add a DLLImport attribute.

In contrast to its name DLLImport imports functions/procedures from .so files on Linux and .dylib files as well.

http://www.mono-project.com/Interop_with_Native_Libraries

P/Invoke in Mono

Answer 2

I know nothing of monotouch, and less about Mac relating to Arm devices, but:

If your lib uses mostly the cdecl calling convention, and monotouch could maybe call cdecl (C) functions over some native operation mechanism (P/Invoke or JNI like stuff), that would be a base principle that could work.

The same for structures, declare with {$packrecords C}.

You might also need to call two functions (IIRC FPC_INITIIALIZE, and another one to finalize) to initialize/finalize the FPC RTL before calling functions.

Anything above the plain C level, such as Delphi Objects and such probably not usable, and must be wrapped. Maybe objective Pascal objects are reusable (at least if monotouch understands objective C ones), but like most other Apple specific stuff, that is not my forte.