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NAME
Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObjTypes,
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 structure
containing information
about the Tcl object
type. This storage must
must live forever, typi-
cally 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.
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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 containes 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 con-
verting 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 representa-
tion 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 function
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 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 typePtr
member to point to the integer type's Tcl_ObjType structure.
The updateStringProc member contains the address of a func-
tion 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. 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 copying its internal representa-
tion 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 incre-
mented 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 internalRep.otherValuePtr
that points to an array of pointers to each element 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 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
representation, type conversion
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