When porting C headers which include function declarations with using char* types. Is it best to use const char* or const(char)* as the type in the D declaration?

22.12.2013 07:47, Gary Willoughby пишет:
> When porting C headers which include function declarations with using
> char* types. Is it best to use const char* or const(char)* as the type
> in the D declaration?
C vs D
const char* == const(char)*
const char const* == const char*

On Sunday, 22 December 2013 at 04:06:05 UTC, Alexandr Druzhinin wrote:
> 22.12.2013 07:47, Gary Willoughby пишет:
>> When porting C headers which include function declarations with using
>> char* types. Is it best to use const char* or const(char)* as the type
>> in the D declaration?
> C vs D
> const char* == const(char)*
> const char const* == const char*

Thanks, that makes sense. But how would i port this parameter:

struct Tcl_Obj * CONST * objv

Maybe like this?:

const Tcl_Obj[]* objv

On Sunday, 22 December 2013 at 15:49:43 UTC, Gary Willoughby wrote:

> Thanks, that makes sense. But how would i port this parameter:

and these:

CONST84 char **tablePtr = ?
CONST84 char ***argvPtr = ?

Am 22.12.2013 17:02, schrieb Gary Willoughby:
> On Sunday, 22 December 2013 at 15:49:43 UTC, Gary Willoughby wrote:
>
>> Thanks, that makes sense. But how would i port this parameter:
>
> and these:
>
> CONST84 char **tablePtr = ?
> CONST84 char ***argvPtr = ?

In C/C++ the const always applies to whatever is left of it. If there is nothing left of it, it applies to what is right to it.

So
"const char**" is equivalent to "char const **". That means the only part that is const is the char. In D const applies to whatever is inside the parantheses.
So the equivalent in D would be

const(char)** and const(char)***

If you have something like the following in C:

const char * const

the D equivalent would be
const(char*)

Note that the star is included in the parantheses here, because the pointer is const to, not only the data it points to.

the D type: const(char**) would be equivalent to C: char const * const * const. (But you won't ever needs this)

Kind Regards
Benjamin Thaut

On Sunday, 22 December 2013 at 16:45:15 UTC, Benjamin Thaut wrote:
> Am 22.12.2013 17:02, schrieb Gary Willoughby:
>> On Sunday, 22 December 2013 at 15:49:43 UTC, Gary Willoughby wrote:
>>
>>> Thanks, that makes sense. But how would i port this parameter:
>>
>> and these:
>>
>> CONST84 char **tablePtr = ?
>> CONST84 char ***argvPtr = ?
>
> In C/C++ the const always applies to whatever is left of it. If there is nothing left of it, it applies to what is right to it.
>
> So
> "const char**" is equivalent to "char const **". That means the only part that is const is the char. In D const applies to whatever is inside the parantheses.
> So the equivalent in D would be
>
> const(char)** and const(char)***
>
> If you have something like the following in C:
>
> const char * const
>
> the D equivalent would be
> const(char*)
>
> Note that the star is included in the parantheses here, because the pointer is const to, not only the data it points to.
>
> the D type: const(char**) would be equivalent to C: char const * const * const. (But you won't ever needs this)
>
> Kind Regards
> Benjamin Thaut

Ah right, so:

struct Tcl_Obj * CONST * objv

would be:

const(Tcl_Obj*)* objv  or  const(Tcl_Obj*)[] objv

Am 22.12.2013 18:39, schrieb Gary Willoughby:
> Ah right, so:
>
> struct Tcl_Obj * CONST * objv
>
> would be:
>
> const(Tcl_Obj*)* objv  or  const(Tcl_Obj*)[] objv

Yes

On Sunday, 22 December 2013 at 18:28:43 UTC, Benjamin Thaut wrote:
> Am 22.12.2013 18:39, schrieb Gary Willoughby:
>> Ah right, so:
>>
>> struct Tcl_Obj * CONST * objv
>>
>> would be:
>>
>> const(Tcl_Obj*)* objv  or  const(Tcl_Obj*)[] objv
>
> Yes

Great thanks! I thought i had a pretty good handle on C but porting some headers makes me scratch my head.

Am 22.12.2013 20:34, schrieb Gary Willoughby:
> On Sunday, 22 December 2013 at 18:28:43 UTC, Benjamin Thaut wrote:
>> Am 22.12.2013 18:39, schrieb Gary Willoughby:
>>> Ah right, so:
>>>
>>> struct Tcl_Obj * CONST * objv
>>>
>>> would be:
>>>
>>> const(Tcl_Obj*)* objv  or  const(Tcl_Obj*)[] objv
>>
>> Yes
>
> Great thanks! I thought i had a pretty good handle on C but porting some
> headers makes me scratch my head.

Yes, its sometimes really astonishing in what ways C-features can be abused. I very recently sumbled apon this:

void (*callbackFunc)(GtkWidget* widget, void* userData);

void registerCallback(callbackFunc func);

void userCallback(GtkEntry* entry)
{
  ...
}

void someFunc()
{
  registerCallback((callbackFunc)&userCallback);
}

Note that the signature of the funciton does not match at all. The first parameter is "casted" automatically to a different data type, which only works because pointers always have the same size and the second paramter is omitted completely. This only works because of the C calling convetion. C can be a strange land ;-)

Kind Regards
Benjamin Thaut

22.12.2013 11:06, Alexandr Druzhinin пишет:
> 22.12.2013 07:47, Gary Willoughby пишет:
>> When porting C headers which include function declarations with using
>> char* types. Is it best to use const char* or const(char)* as the type
>> in the D declaration?
> C vs D
> const char* == const(char)*
> const char const* == const char*
Yes, the last line should be
const char * const == const char*
thanks to Benjamin

IIRC in D qualificator is applied to the right part of statement if there is no the parantheses and to part inside the parantheses if they exists. Important thing is that in D qualificators are transitive. It makes type system more robust (from POV immutability), but doesn't complete it, sadly.