UFFI const, unsigned, opaque-ish types

> On 31 Aug 2016, at 18:59, Ben Coman <[hidden email]> wrote:
>
> For this definition pulled from a library header file...
>    typedef struct {
>        const void *data;
>        unsigned private_flags;
>    } CXString;
>
> which is used with a helper function to get a usable string like...
>  void show_clang_version(void)
>  {    CXString version = clang_getClangVersion();
>       printf("%s\n", clang_getCString(version));
>       clang_disposeString(version);
>  }
>
> ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based on
> LLVM 3.5.0)'
>
>
> So I defined...
>    FFIExternalStructure subclass: #CXString
>        instanceVariableNames: ''
>        classVariableNames: ''
>        package: 'LibCLang'
>
> and ignoring the const as advised in the manual [1],  I try...
>    CXString class >> fieldsDesc
>    ^ #(
>         void *data;
>         unsigned private_flags;
>         )
>
> but...
>    CXString rebuildFieldAccessors.
>    ==>Error: Unable to resolve external type: unsigned
>
> I also tried  "unsigned int private_flags;"
> but get the same error. Any ideas what is wrong?
>
>
> Actually I can kind of ignore creating accessors since this is like an
> opaque type where I'm not expected to access its internals, but I do
> need CXString as a return value like this...
>
>  LibCLang class >> getClangVersion
>     ^ self ffiCall: #( CXString clang_getClangVersion () ) module: LibCLang
>
> which needs to be passed to this function to get a workable string....
>
>  LibCLang class >> getString: aCXString
>     ^ self ffiCall: #( String clang_getCString ( CXString aCXString )
> ) module: LibCLang
>
> However this doesn't work if I use FFIOpaqueObject instead of
> FFIExternalStructure.
> I guess the difference is opaque objects are normally pointers to a
> type, whereas here that pointer is contained in a struct.
>
> What I've done at the moment to push ahead with experimenting is avoid
> needing to generate accessors by adding...
>
>   CXString >> printOn: asStream
>        self getString printOn: aStream
>
>    CXString >> getString
>        ^ self ffiCall: #( String clang_getCString ( CXString self ) )
> module: LibCLang
>
> such that...
>   LibCLang getClangVersion "<Print It>"
>   ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based
> on LLVM 3.5.0)'
>
>
> Is there a better way to approach this?
>
> cheers -ben
>
> btw, this is in Pharo 5 (Moose 6).
>
> [1] https://ci.inria.fr/pharo-contribution/view/Books/job/PharoBookWorkInProgress/lastSuccessfulBuild/artifact/book-result/UnifiedFFI/UnifiedFFI.pdf
>

> Hi,
>
> (Short because I'm by phone)
>
> Const should be ignored so you can keep it (if not is a bug)
> Unsigned does not exist :)
> You can always put an alias, but the type you are looking for is "uint"
>
> Cheers,
> Esteban
>
>> On 31 Aug 2016, at 18:59, Ben Coman <[hidden email]> wrote:
>>
>> For this definition pulled from a library header file...
>>    typedef struct {
>>        const void *data;
>>        unsigned private_flags;
>>    } CXString;
>>
>> which is used with a helper function to get a usable string like...
>>  void show_clang_version(void)
>>  {    CXString version = clang_getClangVersion();
>>       printf("%s\n", clang_getCString(version));
>>       clang_disposeString(version);
>>  }
>>
>> ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based on
>> LLVM 3.5.0)'
>>
>>
>> So I defined...
>>    FFIExternalStructure subclass: #CXString
>>        instanceVariableNames: ''
>>        classVariableNames: ''
>>        package: 'LibCLang'
>>
>> and ignoring the const as advised in the manual [1],  I try...
>>    CXString class >> fieldsDesc
>>    ^ #(
>>         void *data;
>>         unsigned private_flags;
>>         )
>>
>> but...
>>    CXString rebuildFieldAccessors.
>>    ==>Error: Unable to resolve external type: unsigned
>>
>> I also tried  "unsigned int private_flags;"
>> but get the same error. Any ideas what is wrong?
>>
>>
>> Actually I can kind of ignore creating accessors since this is like an
>> opaque type where I'm not expected to access its internals, but I do
>> need CXString as a return value like this...
>>
>>  LibCLang class >> getClangVersion
>>     ^ self ffiCall: #( CXString clang_getClangVersion () ) module: LibCLang
>>
>> which needs to be passed to this function to get a workable string....
>>
>>  LibCLang class >> getString: aCXString
>>     ^ self ffiCall: #( String clang_getCString ( CXString aCXString )
>> ) module: LibCLang
>>
>> However this doesn't work if I use FFIOpaqueObject instead of
>> FFIExternalStructure.
>> I guess the difference is opaque objects are normally pointers to a
>> type, whereas here that pointer is contained in a struct.
>>
>> What I've done at the moment to push ahead with experimenting is avoid
>> needing to generate accessors by adding...
>>
>>   CXString >> printOn: asStream
>>        self getString printOn: aStream
>>
>>    CXString >> getString
>>        ^ self ffiCall: #( String clang_getCString ( CXString self ) )
>> module: LibCLang
>>
>> such that...
>>   LibCLang getClangVersion "<Print It>"
>>   ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based
>> on LLVM 3.5.0)'
>>
>>
>> Is there a better way to approach this?
>>
>> cheers -ben
>>
>> btw, this is in Pharo 5 (Moose 6).
>>
>> [1] https://ci.inria.fr/pharo-contribution/view/Books/job/PharoBookWorkInProgress/lastSuccessfulBuild/artifact/book-result/UnifiedFFI/UnifiedFFI.pdf
>>
>

> On 01 Sep 2016, at 18:40, Ben Coman <[hidden email]> wrote:
>
> Thanks Esteban. That worked.
>
> However it may be good to be more permissive about allowing const to
> reduce the surprises for FFI users.  Same for unsigned.
>
> Reviewing   FFIExternalStructureFIeldParser>>praseFields:structure:
> I see declarations are parsed simply left-to-right, which okay as the
> simplest-thing-that-would-work.   However (in case I get inspired...),
> would this benefit from more complex parsing like described at [1] and
> [2]?  Or is this unlikely to be a concern in prcatice, and/or the rest
> of FFI not ready receive such complex declarations from the parser?
>
> [1] http://www.geeksforgeeks.org/complicated-declarations-in-c/
> [2] http://unixwiz.net/techtips/reading-cdecl.html
>
> cheers -ben
>
> On Thu, Sep 1, 2016 at 2:01 AM, Esteban Lorenzano <[hidden email]> wrote:
>> Hi,
>>
>> (Short because I'm by phone)
>>
>> Const should be ignored so you can keep it (if not is a bug)
>> Unsigned does not exist :)
>> You can always put an alias, but the type you are looking for is "uint"
>>
>> Cheers,
>> Esteban
>>
>>> On 31 Aug 2016, at 18:59, Ben Coman <[hidden email]> wrote:
>>>
>>> For this definition pulled from a library header file...
>>>   typedef struct {
>>>       const void *data;
>>>       unsigned private_flags;
>>>   } CXString;
>>>
>>> which is used with a helper function to get a usable string like...
>>> void show_clang_version(void)
>>> {    CXString version = clang_getClangVersion();
>>>      printf("%s\n", clang_getCString(version));
>>>      clang_disposeString(version);
>>> }
>>>
>>> ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based on
>>> LLVM 3.5.0)'
>>>
>>>
>>> So I defined...
>>>   FFIExternalStructure subclass: #CXString
>>>       instanceVariableNames: ''
>>>       classVariableNames: ''
>>>       package: 'LibCLang'
>>>
>>> and ignoring the const as advised in the manual [1],  I try...
>>>   CXString class >> fieldsDesc
>>>   ^ #(
>>>        void *data;
>>>        unsigned private_flags;
>>>        )
>>>
>>> but...
>>>   CXString rebuildFieldAccessors.
>>>   ==>Error: Unable to resolve external type: unsigned
>>>
>>> I also tried  "unsigned int private_flags;"
>>> but get the same error. Any ideas what is wrong?
>>>
>>>
>>> Actually I can kind of ignore creating accessors since this is like an
>>> opaque type where I'm not expected to access its internals, but I do
>>> need CXString as a return value like this...
>>>
>>> LibCLang class >> getClangVersion
>>>    ^ self ffiCall: #( CXString clang_getClangVersion () ) module: LibCLang
>>>
>>> which needs to be passed to this function to get a workable string....
>>>
>>> LibCLang class >> getString: aCXString
>>>    ^ self ffiCall: #( String clang_getCString ( CXString aCXString )
>>> ) module: LibCLang
>>>
>>> However this doesn't work if I use FFIOpaqueObject instead of
>>> FFIExternalStructure.
>>> I guess the difference is opaque objects are normally pointers to a
>>> type, whereas here that pointer is contained in a struct.
>>>
>>> What I've done at the moment to push ahead with experimenting is avoid
>>> needing to generate accessors by adding...
>>>
>>>  CXString >> printOn: asStream
>>>       self getString printOn: aStream
>>>
>>>   CXString >> getString
>>>       ^ self ffiCall: #( String clang_getCString ( CXString self ) )
>>> module: LibCLang
>>>
>>> such that...
>>>  LibCLang getClangVersion "<Print It>"
>>>  ==> 'Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based
>>> on LLVM 3.5.0)'
>>>
>>>
>>> Is there a better way to approach this?
>>>
>>> cheers -ben
>>>
>>> btw, this is in Pharo 5 (Moose 6).
>>>
>>> [1] https://ci.inria.fr/pharo-contribution/view/Books/job/PharoBookWorkInProgress/lastSuccessfulBuild/artifact/book-result/UnifiedFFI/UnifiedFFI.pdf
>>>
>>
>