[Mono-devel-list] Overcoming PInvoke limitations in e.g. Mono.Posix
sourcejedi at phonecoop.coop
Thu Oct 7 14:45:01 EDT 2004
PInvoke is convenient, but it relies on binary compatability. E.g. much
Posix specifications define symbolic constants for C programs which do not
have a fixed value across all platforms. The layout of structures also
varies between platforms. PInvoke is sufficient for the microsoft world, but
Mono really needs more. As far as I know the current Mono.Posix
implementation doesn't have a complete solution - although I don't know
anything about the SDL or GTK bindings.
I propose a Mono.InteropServices namespace, with tools to write structs and
enums in C# from annotated (with attributes) C# code, with C code as an
intermediate step. The C code would be relatively portable, but the generated
C# code would be platform specific. Already generated C# code could be
included for people without a C compiler (e.g. windows users).
I've been having a go at hand generating some C code first, but I'm quite
willing & able to do the whole thing. Theres only one bit which seems to
involve any actual thinking - typedefs, which can be handled the same way as
in Mono.Posix OEE 0.3:
Quoting Jonathan Pryor jonpryor at vt.edu
> Furthermore, C typedefs get their own types. This feature is debatable,
> and can be changed, but I thought it was cool. Consequently, the C:
> typedef unsigned long size_t;
> Becomes the C#:
> public struct size_t : IComparable, IFormattable...
> private ulong value;
> // ...
> This can get rather tedious, so I have a Perl script which generates the
> structure declarations, stub-vt.pl. (This could also be a shell script,
> or any other language, if that would be preferred. I'm not sure what
> the Mono policy regarding code generation is; I haven't heard of such a
> policy, anyway.)
> The "typedef" classes all support implicit conversions to their
> underlying type, but require explicit conversions back. Usage is thus:
> size_t a = (size_t) (1 + 2);
> size_t b = (size_t) (a + 42);
> // ...
Which sounds fine.
Stop me if this is already being worked on - I know its obvious, it's just
nobody seems to have got around to it yet! Unless I've missed something.
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