The GNUstep CoreBase Library supports the creating of new opaque types through the functions provided by the Runtime Utilities.
Creating new opaque types is easy, but requires some knowledge about structures used internally by the runtime. In particular, a CFRuntimeClass structure will need to be defined and registered with the runtime. The only required fields for this structure is version
and className
. For more information, see the documentation for the CFRuntimeClass structure.
- Note
- This example utilizes functions that are marked as private and may not work across all implementations of the Core Foundation API.
-
Caution should be taken when porting to other implementations.
The opaque type described in this example is a simple container for UInt32 integers. Firstly, define the public interface to the new opaque type. The functions are prefixed with EX
for EXample. This allows for a rudimentary form of namespace.
EXUInt32 type only provides 3 functions:
- Getting the CFTypeID
- Creating a new instance
- Fetch the value associated with this instance
#ifndef __EXUINT32_H__
#define __EXUINT32_H__ 1
#include <CoreFoundation/CFBase.h>
typedef const struct __EXUInt32 *UInt32Ref;
CFTypeID EXUInt32GetTypeID (void);
UInt32 EXUInt32GetValue (EXUInt32Ref u);
#endif
const struct __CFAllocator * CFAllocatorRef
A reference to a CFAllocator object.
Definition CFBase.h:301
The implementation of opaque types require that not only the public interface is implemented, but also the CFRuntimeClass and a structure to represent our EXUInt32Ref instances.
- Note
- The __EXUInt32ClassInitialize() function must be called during initialization of your software. This function registers this opaque type with the runtime.
#include <CoreFoundation/CFBase.h>
#include <CoreFoundation/CFRuntime.h>
#include <CoreFoundation/CFString.h>
#include "EXUInt32.h"
struct __EXUInt32
{
CFRuntimeBase _parent;
UInt32 _value;
};
static Boolean
EXUInt32Equal (CFTypeRef cf1, CFTypeRef cf2)
{
EXUInt32Ref u1 = (EXUInt32Ref) cf1;
EXUInt32Ref u2 = (EXUInt32Ref) cf2;
if (u1->_value == u2->_value)
return true;
return false;
}
EXUInt32Hash (CFTypeRef cf)
{
EXUInt32Ref u = (EXUInt32Ref) cf;
}
static CFStringRef
EXUInt32CopyFormattingDesc (CFTypeRef cf, CFDictionaryRef formatOpts)
{
EXUInt32Ref u = (EXUInt32Ref) cf;
CFSTR (
"%u"), (
unsigned int) u->_value);
}
static CFStringRef
EXUInt32CopyDebugDesc (CFTypeRef cf)
{
EXUInt32Ref u = (EXUInt32Ref) cf;
CFSTR (
"<EXUInt32 %p [%p]>{ value = %u }"),
u, CFGetAllocator (u),
(unsigned int) u->_value);
}
static void
EXUInt32Finalize (CFTypeRef cf)
{
}
static CFTypeID _kEXUInt32TypeID = _kCFRuntimeNotATypeID;
static const CFRuntimeClass _kEXRangeClass = {
0,
"EXUInt32",
NULL,
NULL,
EXUInt32Finalize,
EXUInt32Equal,
EXUInt32Hash,
EXUInt32CopyFormattingDesc,
EXUInt32CopyDebugDesc,
NULL,
NULL
};
void
__EXUInt32ClassInitialize (void)
{
}
CFTypeID
EXUInt32GetTypeID (void)
{
return _kEXUInt32TypeID;
}
EXUInt32Ref
{
struct __EXUInt32 *new;
#define EXUINT32_EXTRA sizeof (struct __EXUInt32) - sizeof (CFRuntimeBase)
EXUINT32REF_EXTRA,
NULL);
if (new)
{
new->_value = value;
}
return new;
}
UInt32
EXUInt32GetValue (EXUInt32Ref u)
{
return u->_value;
}
unsigned long CFHashCode
Definition CFBase.h:159
CFAllocatorRef kCFAllocatorDefault
Definition CFBase.h:334
CFTypeID _CFRuntimeRegisterClass(const CFRuntimeClass *const cls)
CFTypeRef _CFRuntimeCreateInstance(CFAllocatorRef allocator, CFTypeID typeID, CFIndex extraBytes, unsigned char *category)
#define CFSTR(x)
Creates a constant string object.
Definition CFString.h:107