Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 20:42:29 UTC, Luh wrote: Yup that's it ! Many thanks ! One word of warning: ensure the C library does not have the only reference to your Game class instance, or the garbage collector might deallocate it since it does not scan threads created by C libraries. See: https://dlang.org/spec/garbage.html#gc_foreign_obj
Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 19:55:58 UTC, Dennis wrote: On Saturday, 2 November 2019 at 19:42:54 UTC, Luh wrote: So I think I just can't. :( Is that `void* c` in the callback a context pointer by any chance? That's a common thing in C callbacks precisely for purposes like this. You can cast your class to a void* when you register the callback and in the callback function cast it back to a class and call process on that. I don't know what C library you're working with so can't give you specifics. Yup that's it ! Many thanks !
Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 19:42:54 UTC, Luh wrote: So I think I just can't. :( Is that `void* c` in the callback a context pointer by any chance? That's a common thing in C callbacks precisely for purposes like this. You can cast your class to a void* when you register the callback and in the callback function cast it back to a class and call process on that. I don't know what C library you're working with so can't give you specifics.
Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 18:31:28 UTC, Stefan Koch wrote:
On Saturday, 2 November 2019 at 17:49:09 UTC, Luh wrote:
Hello,
When trying to pass a D function to the C callback, the
compiler says:
'Error: cannot implicitly convert expression
of type extern (C) bool delegate(const(short*) a, ulong b,
void* c) to extern (C) bool function(const(short*), ulong,
void*'
because my function is member of a class (compiles when the
function is out of the class).
Is there any way to say to solve this ?
The wiki isn't very clear about the C callbacks:
https://dlang.org/spec/interfaceToC.html#callbacks
C code:
typedef bool (*onProcessCallback)(const short*, size_t, void*);
D Code:
-
class Game
{
onProcessCallback m_onProcessCb;
this()
{
m_onProcessCb = // Error here
}
void onProcess()
{
// ...
}
extern(C) bool onProcessCb(const short* a, size_t b, void* c)
{
onProcess();
return true;
}
}
private extern(C)
{
// Should call onProcess() when executed by the C lib
alias onProcessCallback = bool function(const short*, size_t,
void*);
}
-
you are missing a static in your member function's signature.
The callback is not providing a this pointer.
My problem is, that the onProcess function should not be static
because it uses a variable inside the class.
like:
-
class Game
{
private short[] m_a;
void onProcess(short[] a)
{
m_a ~= a;
// ...
}
extern(C) bool onProcessCb(const short* a, size_t b, void* c)
{
onProcess();
return true;
}
}
-
So I think I just can't. :(
Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 17:49:09 UTC, Luh wrote:
Hello,
When trying to pass a D function to the C callback, the
compiler says:
'Error: cannot implicitly convert expression
of type extern (C) bool delegate(const(short*) a, ulong b,
void* c) to extern (C) bool function(const(short*), ulong,
void*'
because my function is member of a class (compiles when the
function is out of the class).
Is there any way to say to solve this ?
The wiki isn't very clear about the C callbacks:
https://dlang.org/spec/interfaceToC.html#callbacks
C code:
typedef bool (*onProcessCallback)(const short*, size_t, void*);
D Code:
-
class Game
{
onProcessCallback m_onProcessCb;
this()
{
m_onProcessCb = // Error here
}
void onProcess()
{
// ...
}
extern(C) bool onProcessCb(const short* a, size_t b, void* c)
{
onProcess();
return true;
}
}
private extern(C)
{
// Should call onProcess() when executed by the C lib
alias onProcessCallback = bool function(const short*, size_t,
void*);
}
-
This is because onProcessCb is a member of an object. Therefore,
it carries also the information about the context, which includes
e.g. all members of the class.
Due to this onProcessCb is a delegate, which is something
different from a function, cf.
https://dlang.org/spec/function.html#closures
So, there is a type mismatch.
Re: Unable to pass a D function member to a C callback
On Saturday, 2 November 2019 at 17:49:09 UTC, Luh wrote:
Hello,
When trying to pass a D function to the C callback, the
compiler says:
'Error: cannot implicitly convert expression
of type extern (C) bool delegate(const(short*) a, ulong b,
void* c) to extern (C) bool function(const(short*), ulong,
void*'
because my function is member of a class (compiles when the
function is out of the class).
Is there any way to say to solve this ?
The wiki isn't very clear about the C callbacks:
https://dlang.org/spec/interfaceToC.html#callbacks
C code:
typedef bool (*onProcessCallback)(const short*, size_t, void*);
D Code:
-
class Game
{
onProcessCallback m_onProcessCb;
this()
{
m_onProcessCb = // Error here
}
void onProcess()
{
// ...
}
extern(C) bool onProcessCb(const short* a, size_t b, void* c)
{
onProcess();
return true;
}
}
private extern(C)
{
// Should call onProcess() when executed by the C lib
alias onProcessCallback = bool function(const short*, size_t,
void*);
}
-
you are missing a static in your member function's signature.
The callback is not providing a this pointer.
