• Sarath Kumar (53/53) Jan 23 2013 DMD v2.61; openSUSE 12.1
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (53/55) Jan 23 2013 I am assuming that you are interfacing with a C library. That library
• Sarath Kumar (3/31) Jan 24 2013 I don't know the contents of the struct as libA and libB are 3rd
• Mike Parker (5/55) Jan 24 2013 The error message here is deceiving. Declare the struct in one
• Sarath Kumar (8/12) Jan 24 2013 I can't import libA into libB. So, I had moved the forward
• Mike Parker (29/39) Jan 24 2013 The only potential bug I see here is in the error message. What
• Sarath Kumar (9/15) Jan 24 2013 It is a bug because even after casting, the compiler gives an
• Maxim Fomin (40/93) Jan 24 2013 You have hit one of the D problems regarding extern(). The first

"Sarath Kumar" <sarath invalid.com> writes:

DMD v2.61; openSUSE 12.1

Source:
-------
libA.d:

module libA;

extern (C)
{
         struct Opaque;

         Opaque* getObject();

         void doSomething(Opaque *);
}
----------
libB.d:

module libB;

extern (C)
{
         struct Opaque;

         void doAction(Opaque *);
}
-----------
bug.d

import libA, libB;

int main(string[] args)
{
         auto opaque = libA.getObject();
         libA.doSomething(opaque); // this is okay
         libB.doAction(opaque);  // but this is not, compiler 
error here
         return 0;
}

When I compile the above files, I get the below error.
$ rdmd bug.d
bug.d(7): Error: function libB.doAction (Opaque*) is not callable 
using argument types (Opaque*)
bug.d(7): Error: cannot implicitly convert expression (opaque) of 
type Opaque* to Opaque*

If I do an explicit cast, libB.Opaque*, for opaque in line 7, 
bug.d, I get completely different set of errors.

$ rdmd bug.d
libB.d(5): Error: struct libB.Opaque unknown size
libB.d(5): Error: struct libB.Opaque no size yet for forward 
reference
libB.d(5): Error: struct libB.Opaque unknown size
libB.d(5): Error: struct libB.Opaque no size yet for forward 
reference
libA.d(5): Error: struct libA.Opaque unknown size
libA.d(5): Error: struct libA.Opaque no size yet for forward 
reference

Can someone please tell me the right way to pass an opaque object 
between module's functions.

--
Thanks,
Sarath

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 01/23/2013 08:33 AM, Sarath Kumar wrote:

 Can someone please tell me the right way to pass an opaque object
 between module's functions.

I am assuming that you are interfacing with a C library. That library 
must have a D binding file. I am assuming that it is your libA.d:

// libA.d
module libA;

extern (C)
{
         struct Opaque;

         Opaque* getObject();

         void doSomething(Opaque *);
}

There is also a library that implements the struct and the functions. 
Although you would have it in the C library, here is a D module to 
imitate it:

// libA_impl.d
// These are presumably defined in a C library. Simply imitating it with 
this
// D module
extern (C)
{
     struct Opaque
     {
         int i;
         double d;
     }

     Opaque* getObject()
     {
         return new Opaque(42, 1.5);
     }

     void doSomething(Opaque *)
     {}
}

Here is the D module that makes use of that library by importing its D 
binding:

// libB.d
module libB;

import libA;

void doAction(Opaque* o)
{
     doSomething(o);
}

void main()
{
     Opaque* o = getObject();
     doAction(o);
}

Here is how to build the program:

$ dmd libA.d libB.d libA_impl.d -ofmy_prog

Note that normally libA_impl.d would not be included. Instead, the C 
library would be used. For example, if we are talking about a libmy_c_lib.a:

$ dmd libA.d libB.d -L-lmy_c_lib -ofmy_prog

Yes, with the confusing -L in there. ;)

Ali

"Sarath Kumar" <sarath invalid.com> writes:

On Wednesday, 23 January 2013 at 17:14:31 UTC, Ali Çehreli wrote:
 On 01/23/2013 08:33 AM, Sarath Kumar wrote:

 Can someone please tell me the right way to pass an opaque

 object
 between module's functions.

 I am assuming that you are interfacing with a C library. That 
 library must have a D binding file. I am assuming that it is 
 your libA.d:


 There is also a library that implements the struct and the 
 functions. Although you would have it in the C library, here is 
 a D module to imitate it:

 // libA_impl.d
 // These are presumably defined in a C library. Simply 
 imitating it with this
 // D module
 extern (C)
 {
     struct Opaque
     {
         int i;
         double d;
     }

     Opaque* getObject()
     {
         return new Opaque(42, 1.5);
     }

     void doSomething(Opaque *)
     {}
 }

I don't know the contents of the struct as libA and libB are 3rd 
party C libraries.

"Mike Parker" <aldacron gmail.com> writes:

On Wednesday, 23 January 2013 at 16:33:08 UTC, Sarath Kumar wrote:
 DMD v2.61; openSUSE 12.1

 Source:
 -------
 libA.d:

 module libA;

 extern (C)
 {
         struct Opaque;

         Opaque* getObject();

         void doSomething(Opaque *);
 }
 ----------
 libB.d:

 module libB;

 extern (C)
 {
         struct Opaque;

         void doAction(Opaque *);
 }
 -----------
 bug.d

 import libA, libB;

 int main(string[] args)
 {
         auto opaque = libA.getObject();
         libA.doSomething(opaque); // this is okay
         libB.doAction(opaque);  // but this is not, compiler 
 error here
         return 0;
 }

 When I compile the above files, I get the below error.
 $ rdmd bug.d
 bug.d(7): Error: function libB.doAction (Opaque*) is not 
 callable using argument types (Opaque*)
 bug.d(7): Error: cannot implicitly convert expression (opaque) 
 of type Opaque* to Opaque*

 If I do an explicit cast, libB.Opaque*, for opaque in line 7, 
 bug.d, I get completely different set of errors.

 $ rdmd bug.d
 libB.d(5): Error: struct libB.Opaque unknown size
 libB.d(5): Error: struct libB.Opaque no size yet for forward 
 reference
 libB.d(5): Error: struct libB.Opaque unknown size
 libB.d(5): Error: struct libB.Opaque no size yet for forward 
 reference
 libA.d(5): Error: struct libA.Opaque unknown size
 libA.d(5): Error: struct libA.Opaque no size yet for forward 
 reference

 Can someone please tell me the right way to pass an opaque 
 object between module's functions.

The error message here is deceiving. Declare the struct in one 
module only and then import it in every module that uses it. So, 
for example, keep the declaration in libA, remove it from libB 
and in libB add "import libA;".

"Sarath Kumar" <sarath invalid.com> writes:

On Thursday, 24 January 2013 at 09:04:09 UTC, Mike Parker wrote:
 The error message here is deceiving. Declare the struct in one 
 module only and then import it in every module that uses it. 
 So, for example, keep the declaration in libA, remove it from 
 libB and in libB add "import libA;".

I can't import libA into libB. So, I had moved the forward 
declaration into a separate D file and did a public import into 
libA and libB. This works. But this is a workaround. I will file 
a bug.

--
Thanks,
Sarath

"Mike Parker" <aldacron gmail.com> writes:

On Thursday, 24 January 2013 at 09:39:39 UTC, Sarath Kumar wrote:
 On Thursday, 24 January 2013 at 09:04:09 UTC, Mike Parker wrote:
 The error message here is deceiving. Declare the struct in one 
 module only and then import it in every module that uses it. 
 So, for example, keep the declaration in libA, remove it from 
 libB and in libB add "import libA;".

 I can't import libA into libB. So, I had moved the forward 
 declaration into a separate D file and did a public import into 
 libA and libB. This works. But this is a workaround. I will 
 file a bug.

The only potential bug I see here is in the error message. What 
you're seeing is a conflict that arises from D's name mangling. 
The doSomething in libA is expecting a parameter of type 
libA.Opaque* and getObject is returning the same, whereas the 
functions in libB are expecting a parameter of type libB.Opaque*. 
You can see this if you do the following:

writeln(doSomething.mangleof);
writeln(doAction.mangleof);

This is why your code is failing when you call getAction, because 
you're passing it a libA.Opaque* returned from libA.getObject. 
The solution is to declare opaque struct in a single place and 
import it everywhere you need it. That's why your public imports 
work. I would suggest that you not use the public import in this 
case, but work out some other scenario. In Derelict (a collection 
of C bindings) for example, I tend to follow this pattern for any 
lib a bind to:

types.d <- all type & constant declarations go here
functions.d <- all function declarations go here, imports the 
types module

Then I have a module named according to the C library's primary 
header that publicly imports both. For SDL2, for example:

module derelict.sdl2.sdl;

public {
     import derelict.sdl2.types;
     import derelict.sdl2.functions;
}

This way, all types are declared in a single location so there's 
no danger of mixing up different mangles of the same type.

"Sarath Kumar" <sarath invalid.com> writes:

On Thursday, 24 January 2013 at 11:52:57 UTC, Mike Parker wrote:
 The only potential bug I see here is in the error message. What 
 you're seeing is a conflict that arises from D's name mangling. 
 The doSomething in libA is expecting a parameter of type 
 libA.Opaque* and getObject is returning the same, whereas the 
 functions in libB are expecting a parameter of type 
 libB.Opaque*.

   It is a bug because even after casting, the compiler gives an 
error. The compiler wants to know the size of the opaque object, 
even though I'm dealing with a pointer only. As Maxim Fomin 
mentioned, the compiler is trying to create an instance of the 
object even when it is declared as extern (C) and it is a pointer.

--
Thanks,
Sarath

"Maxim Fomin" <maxim maxim-fomin.ru> writes:

On Wednesday, 23 January 2013 at 16:33:08 UTC, Sarath Kumar wrote:
 DMD v2.61; openSUSE 12.1

 Source:
 -------
 libA.d:

 module libA;

 extern (C)
 {
         struct Opaque;

         Opaque* getObject();

         void doSomething(Opaque *);
 }
 ----------
 libB.d:

 module libB;

 extern (C)
 {
         struct Opaque;

         void doAction(Opaque *);
 }
 -----------
 bug.d

 import libA, libB;

 int main(string[] args)
 {
         auto opaque = libA.getObject();
         libA.doSomething(opaque); // this is okay
         libB.doAction(opaque);  // but this is not, compiler 
 error here
         return 0;
 }

 When I compile the above files, I get the below error.
 $ rdmd bug.d
 bug.d(7): Error: function libB.doAction (Opaque*) is not 
 callable using argument types (Opaque*)
 bug.d(7): Error: cannot implicitly convert expression (opaque) 
 of type Opaque* to Opaque*

 If I do an explicit cast, libB.Opaque*, for opaque in line 7, 
 bug.d, I get completely different set of errors.

 $ rdmd bug.d
 libB.d(5): Error: struct libB.Opaque unknown size
 libB.d(5): Error: struct libB.Opaque no size yet for forward 
 reference
 libB.d(5): Error: struct libB.Opaque unknown size
 libB.d(5): Error: struct libB.Opaque no size yet for forward 
 reference
 libA.d(5): Error: struct libA.Opaque unknown size
 libA.d(5): Error: struct libA.Opaque no size yet for forward 
 reference

 Can someone please tell me the right way to pass an opaque 
 object between module's functions.

 --
 Thanks,
 Sarath

You have hit one of the D problems regarding extern(). The first 
problem is that extern(C)-declared objects inside functions are 
still mangled, the other problem is that extern(C) Type var; 
still creates var object, unlike C does (except when Type is a 
function pointer).

The following D program is compiled and linked:

extern(C) int i;

void main()
{
	i = 0;
}

However, a C equivalent would result in linking error due to 
unresolved i reference.

So, what you are really doing is unusable. By the way, doing this 
way you are actually defining two different structs, libA.Opaque 
and libB.Opaque. Compiler is right in this case, because these 
types are incompatible, but it should print full names to show 
the difference explicitly.

If you are working with C library, you can use following scheme:
------main.d------------
extern extern(C) struct Opaque;

extern extern(C) Opaque* getObject();


void main()
{
	Opaque* ptr = getObject();
}
-----struct.c-----------
struct Opaque
{
	int i;
	double d;
};

struct Opaque op;

struct Opaque* getObject()
{
	return &op;
}
------------------------

and if you are using D code, you should use .di files.