ObjectType
Tcl_ObjType(3) Tcl Library Procedures Tcl_ObjType(3)
______________________________________________________________________________
NAME
Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObjTypes, Tcl_Con-
vertToType - manipulate Tcl object types
SYNOPSIS
#include <tcl.h>
Tcl_RegisterObjType(typePtr)
Tcl_ObjType *
Tcl_GetObjType(typeName)
int
Tcl_AppendAllObjTypes(interp, objPtr)
int
Tcl_ConvertToType(interp, objPtr, typePtr)
ARGUMENTS
Tcl_ObjType *typePtr (in) Points to the structure containing
information about the Tcl object
type. This storage must must live
forever, typically by being stati-
cally allocated.
char *typeName (in) The name of a Tcl object type that
Tcl_GetObjType should look up.
Tcl_Interp *interp (in) Interpreter to use for error
reporting.
Tcl_Obj *objPtr (in) For Tcl_AppendAllObjTypes, this
points to the object onto which it
appends the name of each object
type as a list element. For
Tcl_ConvertToType, this points to
an object that must have been the
result of a previous call to
Tcl_NewObj.
_________________________________________________________________
DESCRIPTION
The procedures in this man page manage Tcl object types. The are used
to register new object types, look up types, and force conversions from
one type to another.
Tcl_RegisterObjType registers a new Tcl object type in the table of all
object types supported by Tcl. The argument typePtr points to a
Tcl_ObjType structure that describes the new type by giving its name
and by supplying pointers to four procedures that implement the type.
If the type table already contains a type with the same name as in
typePtr, it is replaced with the new type. The Tcl_ObjType structure
is described in the section THE TCL_OBJTYPE STRUCTURE below.
Tcl_GetObjType returns a pointer to the Tcl_ObjType with name typeName.
It returns NULL if no type with that name is registered.
Tcl_AppendAllObjTypes appends the name of each object type as a list
element onto the Tcl object referenced by objPtr. The return value is
TCL_OK unless there was an error converting objPtr to a list object; in
that case TCL_ERROR is returned.
Tcl_ConvertToType converts an object from one type to another if possi-
ble. It creates a new internal representation for objPtr appropriate
for the target type typePtr and sets its typePtr member to that type.
Any internal representation for objPtr's old type is freed. If an
error occurs during conversion, it returns TCL_ERROR and leaves an
error message in the result object for interp unless interp is NULL.
Otherwise, it returns TCL_OK. Passing a NULL interp allows this proce-
dure to be used as a test whether the conversion can be done (and in
fact was done).
THE TCL_OBJTYPE STRUCTURE
Extension writers can define new object types by defining four proce-
dures, initializing a Tcl_ObjType structure to describe the type, and
calling Tcl_RegisterObjType. The Tcl_ObjType structure is defined as
follows:
typedef struct Tcl_ObjType {
char *name;
Tcl_FreeInternalRepProc *freeIntRepProc;
Tcl_DupInternalRepProc *dupIntRepProc;
Tcl_UpdateStringProc *updateStringProc;
Tcl_SetFromAnyProc *setFromAnyProc;
} Tcl_ObjType;
The name member describes the name of the type, e.g. int. Extension
writers can look up an object type using its name with the Tcl_GetObj-
Type procedure. The remaining four members are pointers to procedures
called by the generic Tcl object code:
The setFromAnyProc member contains the address of a function called to
create a valid internal representation from an object's string repre-
sentation.
typedef int (Tcl_SetFromAnyProc) (Tcl_Interp *interp, Tcl_Obj *objPtr);
If an internal representation can't be created from the string, it
returns TCL_ERROR and puts a message describing the error in the result
object for interp unless interp is NULL. If setFromAnyProc is success-
ful, it stores the new internal representation, sets objPtr's typePtr
member to point to setFromAnyProc's Tcl_ObjType, and returns TCL_OK.
Before setting the new internal representation, the setFromAnyProc must
free any internal representation of objPtr's old type; it does this by
calling the old type's freeIntRepProc if it is not NULL. As an exam-
ple, the setFromAnyProc for the builtin Tcl integer type gets an up-to-
date string representation for objPtr by calling Tcl_GetStringFromObj.
It parses the string to obtain an integer and, if this succeeds, stores
the integer in objPtr's internal representation and sets objPtr's type-
Ptr member to point to the integer type's Tcl_ObjType structure.
The updateStringProc member contains the address of a function called
to create a valid string representation from an object's internal rep-
resentation.
typedef void (Tcl_UpdateStringProc) (Tcl_Obj *objPtr);
objPtr's bytes member is always NULL when it is called. It must always
set bytes non-NULL before returning. We require the string representa-
tion's byte array to have a null after the last byte, at offset length;
this allows string representations that do not contain null bytes to be
treated as conventional null character-terminated C strings. Storage
for the byte array must be allocated in the heap by Tcl_Alloc. Note
that updateStringProcs must allocate enough storage for the string's
bytes and the terminating null byte. The updateStringProc for Tcl's
builtin list type, for example, builds an array of strings for each
element object and then calls Tcl_Merge to construct a string with
proper Tcl list structure. It stores this string as the list object's
string representation.
The dupIntRepProc member contains the address of a function called to
copy an internal representation from one object to another.
typedef void (Tcl_DupInternalRepProc) (Tcl_Obj *srcPtr, Tcl_Obj *dupPtr);
dupPtr's internal representation is made a copy of srcPtr's internal
representation. Before the call, srcPtr's internal representation is
valid and dupPtr's is not. srcPtr's object type determines what copy-
ing its internal representation means. For example, the dupIntRepProc
for the Tcl integer type simply copies an integer. The builtin list
type's dupIntRepProc allocates a new array that points at the original
element objects; the elements are shared between the two lists (and
their reference counts are incremented to reflect the new references).
The freeIntRepProc member contains the address of a function that is
called when an object is freed.
typedef void (Tcl_FreeInternalRepProc) (Tcl_Obj *objPtr);
The freeIntRepProc function can deallocate the storage for the object's
internal representation and do other type-specific processing necessary
when an object is freed. For example, Tcl list objects have an inter-
nalRep.otherValuePtr that points to an array of pointers to each ele-
ment in the list. The list type's freeIntRepProc decrements the refer-
ence count for each element object (since the list will no longer refer
to those objects), then deallocates the storage for the array of point-
ers. The freeIntRepProc member can be set to NULL to indicate that the
internal representation does not require freeing.
SEE ALSO
Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount
KEYWORDS
internal representation, object, object type, string representation,
type conversion
Tcl 8.0 Tcl_ObjType(3)
