plucky (3) Tcl_CopyObjectInstance.3tcl.gz
NAME
Tcl_ClassGetMetadata, Tcl_ClassSetMetadata, Tcl_CopyObjectInstance, Tcl_GetClassAsObject,
Tcl_GetObjectAsClass, Tcl_GetObjectCommand, Tcl_GetObjectFromObj, Tcl_GetObjectName,
Tcl_GetObjectNamespace, Tcl_NewObjectInstance, Tcl_ObjectDeleted, Tcl_ObjectGetMetadata,
Tcl_ObjectGetMethodNameMapper, Tcl_ObjectSetMetadata, Tcl_ObjectSetMethodNameMapper - manipulate objects
and classes
SYNOPSIS
#include <tclOO.h>
Tcl_Object
Tcl_GetObjectFromObj(interp, objPtr)
Tcl_Object
Tcl_GetClassAsObject(class)
Tcl_Class
Tcl_GetObjectAsClass(object)
Tcl_Obj *
Tcl_GetObjectName(interp, object)
Tcl_Command
Tcl_GetObjectCommand(object)
Tcl_Namespace *
Tcl_GetObjectNamespace(object)
Tcl_Object
Tcl_NewObjectInstance(interp, class, name, nsName, objc, objv, skip)
Tcl_Object
Tcl_CopyObjectInstance(interp, object, name, nsName)
int
Tcl_ObjectDeleted(object)
void *
Tcl_ObjectGetMetadata(object, metaTypePtr)
Tcl_ObjectSetMetadata(object, metaTypePtr, metadata)
void *
Tcl_ClassGetMetadata(class, metaTypePtr)
Tcl_ClassSetMetadata(class, metaTypePtr, metadata)
Tcl_ObjectMapMethodNameProc
Tcl_ObjectGetMethodNameMapper(object)
Tcl_ObjectSetMethodNameMapper(object, methodNameMapper)
Tcl_Class │
Tcl_GetClassOfObject(object) │
Tcl_Obj * │
Tcl_GetObjectClassName(interp, object) │
ARGUMENTS
Tcl_Interp *interp (in/out) Interpreter providing the context for looking up or creating an object, and
into whose result error messages will be written on failure.
Tcl_Obj *objPtr (in) The name of the object to look up.
Tcl_Object object (in) Reference to the object to operate upon.
Tcl_Class class (in) Reference to the class to operate upon.
const char *name (in) The name of the object to create, or NULL if a new unused name is to be
automatically selected.
const char *nsName (in) The name of the namespace to create for the object's private use, or NULL if
a new unused name is to be automatically selected. The namespace must not
already exist.
Tcl_Size objc (in) The number of elements in the objv array.
Tcl_Obj *const *objv (in) The arguments to the command to create the instance of the class.
Tcl_Size skip (in) The number of arguments at the start of the argument array, objv, that are
not arguments to any constructors. This allows the generation of correct
error messages even when complicated calling patterns are used (e.g., via
the next command).
Tcl_ObjectMetadataType *metaTypePtr (in)
The type of metadata being set with Tcl_ClassSetMetadata or retrieved with
Tcl_ClassGetMetadata.
void *metadata (in) An item of metadata to attach to the class, or NULL to remove the metadata
associated with a particular metaTypePtr.
Tcl_ObjectMapMethodNameProc methodNameMapper (in)
A pointer to a function to call to adjust the mapping of objects and method
names to implementations, or NULL when no such mapping is required.
________________________________________________________________________________________________________________
DESCRIPTION
Objects are typed entities that have a set of operations ("methods") associated with them. Classes are
objects that can manufacture objects. Each class can be viewed as an object itself; the object view can
be retrieved using Tcl_GetClassAsObject which always returns the object when applied to a non-destroyed
class, and an object can be viewed as a class with the aid of the Tcl_GetObjectAsClass (which either
returns the class, or NULL if the object is not a class). An object may be looked up using the
Tcl_GetObjectFromObj function, which either returns an object or NULL (with an error message in the
interpreter result) if the object cannot be found. The correct way to look up a class by name is to look
up the object with that name, and then to use Tcl_GetObjectAsClass.
Every object has its own command and namespace associated with it. The command may be retrieved using the
Tcl_GetObjectCommand function, the name of the object (and hence the name of the command) with
Tcl_GetObjectName, and the namespace may be retrieved using the Tcl_GetObjectNamespace function. Note
that the Tcl_Obj reference returned by Tcl_GetObjectName is a shared reference. You can also get whether
the object has been marked for deletion with Tcl_ObjectDeleted (it returns true if deletion of the object
has begun); this can be useful during the processing of methods. The class of an object can be retrieved │
with Tcl_GetClassOfObject, and the name of the class of an object with Tcl_GetObjectClassName; note that │
these two may return NULL during deletion of an object (this is transient, and only occurs when the │
object is a long way through being deleted).
Instances of classes are created using Tcl_NewObjectInstance, which creates an object from any class (and
which is internally called by both the create and new methods of the oo::class class). It takes
parameters that optionally give the name of the object and namespace to create, and which describe the
arguments to pass to the class's constructor (if any). The result of the function will be either a
reference to the newly created object, or NULL if the creation failed (when an error message will be left
in the interpreter result). In addition, objects may be copied by using Tcl_CopyObjectInstance which
creates a copy of an object without running any constructors.
Note that the lifetime management of objects is handled internally within TclOO, and does not use
Tcl_Preserve. It is not safe to put a Tcl_Object handle in a C structure with a lifespan different to the
object; you should use the object's command name (as retrieved with Tcl_GetObjectName) instead. It is
safe to use a Tcl_Object handle for the lifespan of a call of a method on that object; handles do not
become invalid while there is an outstanding call on their object (even if the only operation guaranteed
to be safe on them is Tcl_ObjectDeleted; the other operations are only guaranteed to work on non-deleted
objects).
OBJECT AND CLASS METADATA
Every object and every class may have arbitrary amounts of metadata attached to it, which the object or
class attaches no meaning to beyond what is described in a Tcl_ObjectMetadataType structure instance.
Metadata to be attached is described by the type of the metadata (given in the metaTypePtr argument) and
an arbitrary pointer (the metadata argument) that are given to Tcl_ObjectSetMetadata and
Tcl_ClassSetMetadata, and a particular piece of metadata can be retrieved given its type using
Tcl_ObjectGetMetadata and Tcl_ClassGetMetadata. If the metadata parameter to either Tcl_ObjectSetMetadata
or Tcl_ClassSetMetadata is NULL, the metadata is removed if it was attached, and the results of
Tcl_ObjectGetMetadata and Tcl_ClassGetMetadata are NULL if the given type of metadata was not attached.
It is not an error to request or remove a piece of metadata that was not attached.
TCL_OBJECTMETADATATYPE STRUCTURE
The contents of the Tcl_ObjectMetadataType structure are as follows:
typedef const struct {
int version;
const char *name;
Tcl_ObjectMetadataDeleteProc *deleteProc;
Tcl_CloneProc *cloneProc;
} Tcl_ObjectMetadataType;
The version field allows for future expansion of the structure, and should always be declared equal to
TCL_OO_METADATA_VERSION_CURRENT. The name field provides a human-readable name for the type, and is
reserved for debugging.
The deleteProc field gives a function of type Tcl_ObjectMetadataDeleteProc that is used to delete a
particular piece of metadata, and is called when the attached metadata is replaced or removed; the field
must not be NULL.
The cloneProc field gives a function that is used to copy a piece of metadata (used when a copy of an
object is created using Tcl_CopyObjectInstance); if NULL, the metadata will be just directly copied.
TCL_OBJECTMETADATADELETEPROC FUNCTION SIGNATURE
Functions matching this signature are used to delete metadata associated with a class or object.
typedef void Tcl_ObjectMetadataDeleteProc(
void *metadata);
The metadata argument gives the address of the metadata to be deleted.
TCL_CLONEPROC FUNCTION SIGNATURE
Functions matching this signature are used to create copies of metadata associated with a class or
object.
typedef int Tcl_CloneProc(
Tcl_Interp *interp,
void *srcMetadata,
void **dstMetadataPtr);
The interp argument gives a place to write an error message when the attempt to clone the object is to
fail, in which case the clone procedure must also return TCL_ERROR; it should return TCL_OK otherwise.
The srcMetadata argument gives the address of the metadata to be cloned, and the cloned metadata should
be written into the variable pointed to by dstMetadataPtr; a NULL should be written if the metadata is to
not be cloned but the overall object copy operation is still to succeed.
OBJECT METHOD NAME MAPPING
It is possible to control, on a per-object basis, what methods are invoked when a particular method is
invoked. Normally this is done by looking up the method name in the object and then in the class
hierarchy, but fine control of exactly what the value used to perform the look up is afforded through the
ability to set a method name mapper callback via Tcl_ObjectSetMethodNameMapper (and its introspection
counterpart, Tcl_ObjectGetMethodNameMapper, which returns the current mapper). The current mapper (if
any) is invoked immediately before looking up what chain of method implementations is to be used.
TCL_OBJECTMAPMETHODNAMEPROC FUNCTION SIGNATURE
The Tcl_ObjectMapMethodNameProc callback is defined as follows:
typedef int Tcl_ObjectMapMethodNameProc(
Tcl_Interp *interp,
Tcl_Object object,
Tcl_Class *startClsPtr,
Tcl_Obj *methodNameObj);
If the result is TCL_OK, the remapping is assumed to have been done. If the result is TCL_ERROR, an error
message will have been left in interp and the method call will fail. If the result is TCL_BREAK, the
standard method name lookup rules will be used; the behavior of other result codes is currently
undefined. The object parameter says which object is being processed. The startClsPtr parameter points to
a variable that contains the first class to provide a definition in the method chain to process, or NULL
if the whole chain is to be processed (the argument itself is never NULL); this variable may be updated
by the callback. The methodNameObj parameter gives an unshared object containing the name of the method
being invoked, as provided by the user; this object may be updated by the callback.
REFERENCE COUNT MANAGEMENT
The objPtr argument to Tcl_GetObjectFromObj will not have its reference count manipulated, but this
function may modify the interpreter result (to report any error) so interpreter results should not be fed
into this without an additional reference being used.
The result of Tcl_GetObjectName is a value that is owned by the object that is regenerated when this
function is first called after the object is renamed. If the value is to be retained at all, the caller
should increment the reference count.
The first objc values in the objv argument to Tcl_NewObjectInstance are the arguments to pass to the
constructor. They must have a reference count of at least 1, and may have their reference counts changed
during the running of the constructor. Constructors may modify the interpreter result, which consequently
means that interpreter results should not be used as arguments without an additional reference being
taken.
The methodNameObj argument to a Tcl_ObjectMapMethodNameProc implementation will be a value with a
reference count of at least 1 where at least one reference is not held by the interpreter result. It is
expected that method name mappers will only read their methodNameObj arguments.
SEE ALSO
Method(3tcl), oo::class(3tcl), oo::copy(3tcl), oo::define(3tcl), oo::object(3tcl)
KEYWORDS
class, constructor, object