Provide CFUNCTYPE prototype name for function pointers defined in Structure

[GoogleCodeExporter]

When wrapping a function pointer inside a structure, there is not corresponding 
CFUNCTYPE prototype type provided so we can initialize the prototype. Like

struct ui_interface {
    void (*post_warning)(const char *title,const char *statement,...);
    char *(*open_file)(const char *title, const char *defaultfile,
        const char *initial_filter);
}

ctypesgen correctly defined the types for post_warning and open_file as
functype like:

struct_ui_interface._fields_ = [
    ('post_warning', CFUNCTYPE(UNCHECKED(None), String, String)),
    ('open_file', CFUNCTYPE(UNCHECKED(String), String, String, String)),
]

But it should provide struct_ui_interface_post_warning_func and
struct_ui_interface_open_file_func so that we can create the CFUNCTYPE object
easily.

struct_ui_interface_post_warning_func =  CFUNCTYPE(UNCHECKED(None), String, 
String))

struct_ui_interface_open_file_func = CFUNCTYPE(UNCHECKED(String), String, 
String, String))

Original issue reported on code.google.com by mozbug...@gmail.com on 21 May 2011 at 12:42

[Alan-R]

I've certainly run into this myself. It would be handy, and not inconsistent with ctypesgen goals (IMHO).

[mara004]

If I understood this correctly, I'm facing the same in my project. This is my current solution:

def set_callback(struct, fname, callback):
    # hack to extract CFUNCTYPE definition and wrap callback
    setattr(struct, fname, type(getattr(struct, fname))(callback))

Example usage:

# `_buffer_writer` is a callable factory, and `buffer` an io.BufferedReader or similar
writer = pdfium_c.FPDF_FILEWRITE(version=1)
set_callback(writer, "WriteBlock", _buffer_writer(buffer))

It's none too nice this is left to the caller. Ideally, assigning a function to a field should just do the CFUNCTYPE wrapping automatically, if that were possible to implement in ctypes/python.

I don't think such templates belong in ctypesgen, though. Maybe rather in a separate ctypes-extensions package or something, if need be. But overall standalone ctypes is fairly complete these days.