Re: Example Ada calling Gnu Scientific Library (GSL)

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2017-04-10 17:39, hreba wrote:
> On 04/10/2017 11:47 AM, Dmitry A. Kazakov wrote:
>>
>> You also seem confuse project to build and project to use a library.
>> They are not same! For a bindings library you need both.
>>
>
> I don't understand that. From the discussions here on the list I thought:
>
> 1. Thin binding is just an interface module which allows to call the C
> library functions from an Ada program, using all the parameters of the C
> prototype and some types from Interfaces.C.
> Library project.

Yes, plus conversion of some elementary types. It is considered thin to 
convert char * to String and int!=0 to Boolean.

> 2. Thick binding: Specification and implementation of Ada subprograms
> which call subprograms of the thin binding. Interfaces.C types can be
> avoided in the specifications. Specification of exported subprograms
> usually differ from corresponding imported C prototypes, because this is
> what you want from thick bindings.
> Library project, because there is no executable.

Yes.

> 3. Application calls subprograms from the thick binding and defines
> executable(s) (Main).
> Non-library project because executables are generated.

AFAIK relocatable library counts as executable, but yes.

> What is wrong here, why do i need both types of projects for a bindings
> library?

It is how gprbuild works. I am not happy with that design but it is how 
it is.

You need:

1. C library project [or package Linker / Library_Options]

2.a. Ada thin bindings library build project that with-es #1
2.b. Ada thin bindings library use project that with-es #1

3.a. Ada think bindings library build project that with-es #2.b
3.b. Ada think bindings library use project that with-es #2.b

4. Application build project that with-es #3.b

You can ditch #1 and then:

for #2.a you use package Linker to link to C library
for #2.b you use Linker_Options to instruct future users of the library 
that they also must link to the C library

To summarize: for building application or library you use different 
options from when you use already built library in another project.

Of course, 2 and 3 are normally merged together. There is little reason 
to keep them in separate libraries.

> And is that documented anywhere?

Sure, you can find hints in:

https://docs.adacore.com/gprbuild-docs/html/gprbuild_ug/gnat_project_manager.html

P.S. For an example of thin and thick bindings smaller than GtkAda you 
can look at ODBC bindings:

http://www.dmitry-kazakov.de/ada/components.htm#ODBC_Bindings

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de