Tcl_Class(3) TclOO Library Functions Tcl_Class(3)

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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)

ClientData
Tcl_ObjectGetMetadata(object, metaTypePtr)

Tcl_ObjectSetMetadata(object, metaTypePtr, metadata)

ClientData
Tcl_ClassGetMetadata(class, metaTypePtr)

Tcl_ClassSetMetadata(class, metaTypePtr, metadata)

Tcl_ObjectMapMethodNameProc
Tcl_ObjectGetMethodNameMapper(object)

Tcl_ObjectSetMethodNameMapper(object, methodNameMapper)

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.

int 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.

int 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.

ClientData 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.
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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.

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(
ClientData 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,
ClientData srcMetadata,
ClientData *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.

SEE ALSO

Method(3), oo::class(n), oo::copy(n), oo::define(n), oo::object(n)

KEYWORDS

class, constructor, object

TclOO 0.1 Tcl_Class(3)