ADC Home > Reference Library > Reference > Darwin > Kernel Framework Reference

OSMetaClassBase

Inherits from:	class
Declared In:	OSMetaClass.h

Overview

OSMetaClassBase is the abse class for libkern data types.

Functions

getRetainCount: Gets the number of times this object has been retained.
isEqualTo: Returns whether 'this' == anObj.
metaCast(const char *): See OSMetaClassBase::metaCast(const OSMetaClass *).
metaCast(const OSMetaClass *): Checks to see if this object is or inherits from the given type.
metaCast(const OSString *): See OSMetaClassBase::metaCast(const OSMetaClass *).
metaCast(const OSSymbol *): See OSMetaClassBase::metaCast(const OSMetaClass *).
operator =: Disables implicit copy constructor by making private.
OSMetaClassBase: Disables implicit copy constructor by making private.
release(): Releases a reference to this object.
release(int): Primary implementation of the release mechanism.
retain: Retains a reference to this object.
serialize: Archives the receiver.
taggedRelease(const void *): Releases a tagged reference to this object
taggedRelease(const void *, const int): Releases a tagged reference to this object and free if retainCount == 'when' on entry.
taggedRetain: Retains a tagged reference to this object.

isEqualTo

Returns whether 'this' == anObj.

public

virtual bool isEqualTo(
    const OSMetaClassBase *anObj) const;

Parameters

anObj: Object to compare 'this' to.

Return Value

Returns true if the objects are equivalent, false otherwise.

Discussion

OSMetaClassBase::isEqualTo implements this as a shallow pointer comparison. The OS container classes do a more meaningful comparison. Your mileage may vary.

metaCast(const char *)

See OSMetaClassBase::metaCast(const OSMetaClass *).

public

OSMetaClassBase *metaCast(
    const char *toMeta) const;

Parameters

toMeta: const char * C String of the desired class' name.

Return Value

Returns 'this' if the object is of the desired type, otherwise 0.

metaCast(const OSMetaClass *)

Checks to see if this object is or inherits from the given type.

public

OSMetaClassBase *metaCast(
    const OSMetaClass *toMeta) const;

Parameters

toMeta: Pointer to a constant OSMetaClass for the desired target type.

Return Value

Returns 'this' if the object is of the desired type, otherwise 0.

Discussion

This function is the guts of the OSMetaClass system. IODynamicCast, qv, is implemented using this function.

metaCast(const OSString *)

See OSMetaClassBase::metaCast(const OSMetaClass *).

public

OSMetaClassBase *metaCast(
    const OSString *toMeta) const;

Parameters

toMeta: OSString of the desired class' name.

Return Value

Returns 'this' if the object is of the desired type, otherwise 0.

metaCast(const OSSymbol *)

See OSMetaClassBase::metaCast(const OSMetaClass *).

public

OSMetaClassBase *metaCast(
    const OSSymbol *toMeta) const;

Parameters

toMeta: OSSymbol of the desired class' name.

Return Value

Returns 'this' if the object is of the desired type, otherwise 0.

operator =

Disables implicit copy constructor by making private.

private

void operator =(
    OSMetaClassBase &src);

Parameters

src: Reference to source object that isn't allowed to be copied.

OSMetaClassBase

Disables implicit copy constructor by making private.

private

OSMetaClassBase(
    OSMetaClassBase &src);

Parameters

src: Reference to source object that isn't allowed to be copied.

release()

Releases a reference to this object.

public

virtual void release() const = 0;

release(int)

Primary implementation of the release mechanism.

public

virtual void release(
    int when) const = 0;

Parameters

when: When retainCount == 'when' then call free().

Discussion

If retainCount

retain

Retains a reference to this object.

public

virtual void retain() const = 0;

serialize

Archives the receiver.

public

virtual bool serialize(
    OSSerialize *s) const = 0;

Parameters

s: The OSSerialize object.

Return Value

Returns true if serialization was successful, false if not.

taggedRelease(const void *)

Releases a tagged reference to this object

public

virtual void taggedRelease(
    const void *tag = 0) const = 0;

taggedRelease(const void *, const int)

Releases a tagged reference to this object and free if retainCount == 'when' on entry.

protected

virtual void taggedRelease(
    const void *tag,
    const int when) const = 0;

taggedRetain

Retains a tagged reference to this object.

public

virtual void taggedRetain(
    const void *tag = 0) const = 0;

#defines

OSCheckTypeInst

Is the target object a subclass of the reference object?

#define OSCheckTypeInst(typeinst, inst) \ 
    OSMetaClassBase::checkTypeInst(inst, typeinst)

Parameters

typeinst: Reference instance of an object, desired type.
inst: Instance of object to check for type compatibility.

Return Value

false if typeinst or inst are 0 or inst is not a subclass of typeinst's class. true otherwise.

OSDynamicCast

Roughly analogous to (type *) inst, but check if valid first.

#define OSDynamicCast(type, inst) \ 
    ((type *) OSMetaClassBase::safeMetaCast((inst), (type::metaClass)))

Parameters

type: name of desired class name. Notice that it is assumed that you desire to cast to a pointer to an object of this type. Also type qualifiers, like const, are not recognized and will cause an, usually obscure, compile error.
inst: Pointer to object that you wish to attempt to type cast. May be 0.

Return Value

inst if object non-zero and it is of the desired type, otherwise 0.

Discussion

OSDynamicCast is an attempt to implement a rudimentary equivalent to rtti's dynamic_cast operator. Embedded-C++ doesn't allow the use of rtti. OSDynamicCast is build on the OSMetaClass mechanism. Note it is safe to call this with a 0 parameter.

OSMemberFunctionCast

Converts a pointer to a member function to a C-style pointer to function (note that no warnings are generated).

#define OSMemberFunctionCast(cptrtype, self, func) \ 
    (cptrtype) OSMetaClassBase:: \ 
    _ptmf2ptf(self, (void (OSMetaClassBase::*)(void)) func)

Parameters

cptrtype: The type of pointer function desired.
self: The 'this' pointer of the object whose function you wish to cache.
func: The pointer to the member function itself, something like &Base::func.

Return Value

Returns a pointer to function of the given type. This function will panic if an attempt is made to call it with a multiply inherited class.

OSTypeAlloc

Allocate an instance of the desired object.

#define OSTypeAlloc(type)

Parameters

type: Name of the desired type to be created.

Return Value

'this' if object cas been successfully created.

Discussion

The OSTypeAlloc macro can be used to break the binary compatibility difficulties presented by new. The problem is that C++ compiles the knowledge of the size of the class into the cade calling new. If you use the alloc code however the class size is determined by the callee not the caller.

OSTypeID

Given the name of a class return it's typeID

#define OSTypeID(type)

Parameters

type: Name of the desired type, eg. OSObject.

Return Value

A unique Type ID for the class.

OSTypeIDInst

Given a pointer to an object return it's typeID

#define OSTypeIDInst(typeinst)

Parameters

typeinst: An instance of an OSObject subclass.

Return Value

The typeID, ie. OSMetaClass *.

Did this document help you?

Yes: Tell us what works for you.

It’s good, but: Report typos, inaccuracies, and so forth.

It wasn’t helpful: Tell us what would have helped.

Last Updated: 2008-12-19