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Tcl_ObjType(3) Tcl Library Procedures Tcl_ObjType(3)
_________________________________________________________________________________________________
NAME
Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObjTypes, Tcl_ConvertToType - manipu-
late 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 live forever,
typically by being statically allocated.
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_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. They 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 that
Tcl_GetObjType can look up by name. There are other object types supported by Tcl as
well, which Tcl chooses not to register. Extensions can likewise choose to register the
object types they create or not. The argument typePtr points to a Tcl_ObjType structure
that describes the new type by giving its name and by supplying pointers to four proce-
dures 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 registered Tcl_ObjType with name typeName. It
returns NULL if no type with that name is registered.
Tcl_AppendAllObjTypes appends the name of each registered 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 representation for objPtr appropriate for the target type typePtr and sets
its typePtr member as determined by calling the typePtr->setFromAnyProc routine. Any
internal representation for objPtr's old type is freed. If an error occurs during conver-
sion, 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). |
In many cases, the typePtr->setFromAnyProc routine will set objPtr->typePtr to the argu- |
ment value typePtr, but that is no longer guaranteed. The setFromAnyProc is free to set |
the internal representation for objPtr to make use of another related Tcl_ObjType, if it |
sees fit.
THE TCL_OBJTYPE STRUCTURE
Extension writers can define new object types by defining four procedures and initializing
a Tcl_ObjType structure to describe the type. Extension writers may also pass a pointer
to their Tcl_ObjType structure to Tcl_RegisterObjType if they wish to permit other exten-
sions to look up their Tcl_ObjType by name with the Tcl_GetObjType routine. The Tcl_Obj-
Type 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 FIELD
The name member describes the name of the type, e.g. int. When a type is registered, this
is the name used by callers of Tcl_GetObjType to lookup the type. For unregistered types,
the name field is primarily of value for debugging. The remaining four members are point-
ers to procedures called by the generic Tcl object code:
THE SETFROMANYPROC FIELD
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 cannot 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 the Tcl_ObjType struct corresponding to the new internal repre-
sentation, 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 setFromAnyProc for the built-in Tcl list type gets an up-to-date string
representation for objPtr by calling Tcl_GetStringFromObj. It parses the string to verify
it is in a valid list format and to obtain each element value in the list, and, if this
succeeds, stores the list elements in objPtr's internal representation and sets objPtr's
typePtr member to point to the list type's Tcl_ObjType structure.
Do not release objPtr's old internal representation unless you replace it with a new one
or reset the typePtr member to NULL.
The setFromAnyProc member may be set to NULL, if the routines making use of the internal
representation have no need to derive that internal representation from an arbitrary
string value. However, in this case, passing a pointer to the type to Tcl_ConvertToType()
will lead to a panic, so to avoid this possibility, the type should not be registered.
THE UPDATESTRINGPROC FIELD
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, and to have no null bytes before that; this allows string
representations to be treated as conventional null character-terminated C strings. These
restrictions are easily met by using Tcl's internal UTF encoding for the string represen-
tation, same as one would do for other Tcl routines accepting string values as arguments.
Storage for the byte array must be allocated in the heap by Tcl_Alloc or ckalloc. Note
that updateStringProcs must allocate enough storage for the string's bytes and the termi-
nating null byte.
The updateStringProc for Tcl's built-in double type, for example, calls Tcl_PrintDouble to
write to a buffer of size TCL_DOUBLE_SPACE, then allocates and copies the string represen-
tation to just enough space to hold it. A pointer to the allocated space is stored in the
bytes member.
The updateStringProc member may be set to NULL, if the routines making use of the internal
representation are written so that the string representation is never invalidated. Fail-
ure to meet this obligation will lead to panics or crashes when Tcl_GetStringFromObj or
other similar routines ask for the string representation.
THE DUPINTREPPROC FIELD
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 representation means.
For example, the dupIntRepProc for the Tcl integer type simply copies an integer. The
built-in list type's dupIntRepProc uses a far more sophisticated scheme to continue shar-
ing storage as much as it reasonably can.
THE FREEINTREPPROC FIELD
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 represen-
tation and do other type-specific processing necessary when an object is freed.
For example, the list type's freeIntRepProc respects the storage sharing scheme estab-
lished by the dupIntRepProc so that it only frees storage when the last object sharing it
is being freed.
The freeIntRepProc member can be set to NULL to indicate that the internal representation
does not require freeing. The freeIntRepProc implementation must not access the bytes
member of the object, since Tcl makes its own internal uses of that field during object
deletion. The defined tasks for the freeIntRepProc have no need to consult the bytes mem-
ber.
SEE ALSO
Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount
KEYWORDS
internal representation, object, object type, string representation, type conversion
Tcl 8.0 Tcl_ObjType(3)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache
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2024-04-18 22:04 @3.138.175.180 CrawledBy Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)