[Mono-list] Interop Utility

[Jonathan Pryor]

On Wed, 2005-11-30 at 18:10 -0500, Abe Gillespie wrote:
> I seem to remember there was something lightweight out there where you
> might choose just one function in a C library and the utility would
> write the function declaration for you.  Am I making this up?

I haven't seen such a utility, largely because such a utility is
non-trivial.  Consider a C `char*' parameter -- there are no less than
*six* potential C# bindings for it: string (if you know it won't be
modified), StringBuilder (if it's an output buffer), sbyte[] (for raw
binary data or "strings" in an unknown encoding), and IntPtr or void* or
sbyte* for raw pointer behavior.

How's a generator supposed to know which is appropriate?  It can't.  It
requires human interpretation of documentation (or the function's source
code) to determine which C# binding is appropriate.  See also:

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

Strings are just the beginning.  Anything dealing with structures is a
world of hurt.  At best you can do it entirely in C#, at worst you'll
need a C glue layer (see MonoPosixHelper, which provides glue code for a
number of C structures, and *must* do so because the size/ordering of
POSIX structures is implementation dependent).

Show me a program that handles the above, and I'll show you something
that isn't fully covering all the potential corner cases. :-)

An easier program would be a C# -> C glue code generator, since C#->C
doesn't have as many contextual problems.  Add in some custom
attributes, and glue code becomes somewhat easier to deal with.
(Mono.Posix does this to some extent with the make-map.exe program,
which is used to generate enumeration translation functions and function
prototypes for the P/Invoke functions.  It's not a general-purpose
program either, though.)

 - Jon