Re: Ada as glue ? logical approach ?

[Brian Drummond <brian@shapes.demon.co.uk>]

On Sat, 28 Jan 2012 20:53:21 -0800, Patrick wrote:

> Hi Everyone
> 
> I have been studying ada for sometime now but I have no experience
> coding with it.
> 
>  It doesn't look like there are all the library bindings i want but I
> am wondering if this really matters.
> 
> Someone could write a full binding for a library but could someone also
> not just use the import pragma to "grab onto" the existing C library
> APIs?
> 
> This would be a bit like ctypes in Python correct ? Are other list
> members writing their own 'as needed' partial bindings? Is this a
> logical approach? -Patrick

In addition to agreeing with the other comments - especially the 
recommendation to make a "thick binding" to give you an Ada-like 
interface, rather than exposing the C-like details any more widely than 
necessary...

if you use a recent enough version of GCC, you can compile a C or C++ 
header file with the -fdump-ada-spec or -fdump-ada-spec-slim options, and 
it will automatically generate the thin binding (with import pragmas) for 
you. The -slim version just compiles the header you give it; the fat 
version compiles the transitive closure (i.e. all the header files it 
imports too, recursively)

The result is not perfect; very good on plain C but it doesn't handle C++ 
templates very well (last time I looked) but even then, it saves a lot of 
time.

I would implement the Ada binding as a package that uses this, exposing 
only Ada types and functions to the rest of your code.

A very simple example : 
http://wiki.ada-dk.org/c_bindings_example

If you are importing C rather than C++, ignore the bit about saving the 
header as .hpp. (There is another way to force C vs C++, not covered in 
the article. Compile a .h file with g++ rather than gcc)

See also 
http://www.adacore.com/2009/02/23/gem-59/

- Brian