[Development] Could support for C be added to Qt?

[samuel ammonius]

Hello,

I'm new to contributing to Qt directly, but I've been trying to create
external C bindings for Qt for a few months now. Since C and C++ are so
similar, I've recently been thinking it may just be better to add C support
directly to the Qt headers by checking for the __cplusplus macro.

The design I was thinking of in particular was to put a function macro in
qtglobals.h for creating C aliases for C++ functions (I'll call the macro
QT_C_EXPORT for now).

#ifdef __cplusplus
#  define QT_C_EXPORT(RETURN_TYPE, A, B, PARAMS) extern "C" const auto B
#else
#  define QT_C_EXPORT(RETURN_TYPE, A, B, PARAMS) RETURN_TYPE B PARAMS
#endif

#define QT_DEFINE_C_EXPORT(RETURN_TYPE, A, B, PARAMS) extern "C" const auto
B = &##A

Then it can be used like this:

________________________________________________________________
[qpushbutton.h]
#ifdef __cplusplus

class QPushButton {...};

#else

typedef struct QPushButton QPushButton;

QT_C_EXPORT(void, QPushButton::setFlat, QPushButton_setFlat, (bool));


[qpushbutton.cpp]
// functions...
QT_DEFINE_C_EXPORT(void, QPushButton::setFlat, QPushButton_setFlat, (bool));
________________________________________________________________

There's a couple things I still haven't figured out though, like
constructors/destructors and templates. Are there solutions to these that
would still allow support to be added to Qt internally or would external
bindings be better?
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