Tcl_ObjType (3)
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 *typeName in
Tcl_ObjType *typePtr in
Points to the structure containing information about the Tcl object type.
This storage must must live forever,
typically by being statically 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 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
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 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 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 example, 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 typePtr 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 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 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 internalRep.otherValuePtr
that points to an array of pointers to each element in the list.
The list type's freeIntRepProc decrements
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 representation, type conversion
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