tcl_objtype(3)

NAME

Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObj
Types, Tcl_ConvertToType - 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 struc

ture containing infor
mation about the Tcl
object type. This
storage must live for
ever, typically by
being statically allo
cated.

CONST 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_AppendAllObj

Types, 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_Obj Type 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 possible. It creates a new internal represen
tation 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 procedure 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 procedures, 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_GetObjType procedure. The remaining four members are pointers to procedures called by the
generic Tcl object code:

The setFromAnyProc member contains the address of a func tion called to create a valid internal representation from
an object's string representation.

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 successful, 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 set_
FromAnyProc 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 example, the set_ FromAnyProc for the builtin Tcl integer type gets an upto-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 typePtr member to point to the integer type's Tcl_ObjType struc
ture. Do not release objPtr's old internal representation unless you replace it with a new one or reset the typePtr member to NULL.

The updateStringProc member contains the address of a function called to create a valid string representation
from an object's internal representation.

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 representation'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 or ckalloc. Note that updateString_ Procs 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 representa
tion.

The dupIntRepProc member contains the address of a func tion 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 copying its internal representation means. For example, the dupIn_
tRepProc for the Tcl integer type simply copies an inte ger. 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 ref
erence counts are incremented to reflect the new refer
ences).

The freeIntRepProc member contains the address of a func tion 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 typespecific processing necessary when an object is freed.
For example, Tcl list objects have an internalRep.other_ ValuePtr that points to an array of pointers to each ele ment in the list. The list type's freeIntRepProc decre ments the reference count for each element object (since
the list will no longer refer to those objects), then
deallocates the storage for the array of pointers. 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 rep
resentation, type conversion

Tcl 8.0 Tcl_ObjType(3)