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.so man.macros

.TH Tcl_ObjType 3 8.0 Tcl "Tcl Library Procedures"

.BS

.SH NAME

Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObjTypes, Tcl_ConvertToType  \- manipulate Tcl object types

.SH SYNOPSIS

.nf

\fB#include \fR

.sp

\fBTcl_RegisterObjType\fR(\fItypePtr\fR)

.sp

Tcl_ObjType *

\fBTcl_GetObjType\fR(\fItypeName\fR)

.sp

int

\fBTcl_AppendAllObjTypes\fR(\fIinterp, objPtr\fR)

.sp

int

\fBTcl_ConvertToType\fR(\fIinterp, objPtr, typePtr\fR)

.SH ARGUMENTS

.AS Tcl_ObjType *typeName in

.AP 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.

.AP char *typeName in

The name of a Tcl object type that \fBTcl_GetObjType\fR should look up.

.AP Tcl_Interp *interp in

Interpreter to use for error reporting.

.AP Tcl_Obj *objPtr in

For \fBTcl_AppendAllObjTypes\fR, this points to the object onto which

it appends the name of each object type as a list element.

For \fBTcl_ConvertToType\fR, this points to an object that

must have been the result of a previous call to \fBTcl_NewObj\fR.

.BE

.SH DESCRIPTION

.PP

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.

.PP

\fBTcl_RegisterObjType\fR registers a new Tcl object type

in the table of all object types supported by Tcl.

The argument \fItypePtr\fR 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 \fItypePtr\fR,

it is replaced with the new type.

The Tcl_ObjType structure is described

in the section \fBTHE TCL_OBJTYPE STRUCTURE\fR below.

.PP

\fBTcl_GetObjType\fR returns a pointer to the Tcl_ObjType

with name \fItypeName\fR.

It returns NULL if no type with that name is registered.

.PP

\fBTcl_AppendAllObjTypes\fR appends the name of each object type

as a list element onto the Tcl object referenced by \fIobjPtr\fR.

The return value is \fBTCL_OK\fR unless there was an error

converting \fIobjPtr\fR to a list object;

in that case \fBTCL_ERROR\fR is returned.

.PP

\fBTcl_ConvertToType\fR converts an object from one type to another

if possible.

It creates a new internal representation for \fIobjPtr\fR

appropriate for the target type \fItypePtr\fR

and sets its \fItypePtr\fR member to that type.

Any internal representation for \fIobjPtr\fR's old type is freed.

If an error occurs during conversion, it returns \fBTCL_ERROR\fR

and leaves an error message in the result object for \fIinterp\fR

unless \fIinterp\fR is NULL.

Otherwise, it returns \fBTCL_OK\fR.

Passing a NULL \fIinterp\fR allows this procedure to be used

as a test whether the conversion can be done (and in fact was done).

.SH "THE TCL_OBJTYPE STRUCTURE"

.PP

Extension writers can define new object types by defining four

procedures,

initializing a Tcl_ObjType structure to describe the type,

and calling \fBTcl_RegisterObjType\fR.

The \fBTcl_ObjType\fR structure is defined as follows:

.CS

typedef struct Tcl_ObjType {

        char *\fIname\fR;

        Tcl_FreeInternalRepProc *\fIfreeIntRepProc\fR;

        Tcl_DupInternalRepProc *\fIdupIntRepProc\fR;

        Tcl_UpdateStringProc *\fIupdateStringProc\fR;

        Tcl_SetFromAnyProc *\fIsetFromAnyProc\fR;

} Tcl_ObjType;

.CE

.PP

The \fIname\fR member describes the name of the type, e.g. \fBint\fR.

Extension writers can look up an object type using its name

with the \fBTcl_GetObjType\fR procedure.

The remaining four members are pointers to procedures

called by the generic Tcl object code:

.PP

The \fIsetFromAnyProc\fR member contains the address of a function

called to create a valid internal representation

from an object's string representation.

.CS

typedef int (Tcl_SetFromAnyProc) (Tcl_Interp *\fIinterp\fR, Tcl_Obj *\fIobjPtr\fR);

.CE

If an internal representation can't be created from the string,

it returns \fBTCL_ERROR\fR and puts a message

describing the error in the result object for \fIinterp\fR

unless \fIinterp\fR is NULL.

If \fIsetFromAnyProc\fR is successful,

it stores the new internal representation,

sets \fIobjPtr\fR's \fItypePtr\fR member to point to

\fIsetFromAnyProc\fR's \fBTcl_ObjType\fR, and returns \fBTCL_OK\fR.

Before setting the new internal representation,

the \fIsetFromAnyProc\fR must free any internal representation

of \fIobjPtr\fR's old type;

it does this by calling the old type's \fIfreeIntRepProc\fR

if it is not NULL.

As an example, the \fIsetFromAnyProc\fR for the builtin Tcl integer type

gets an up-to-date string representation for \fIobjPtr\fR

by calling \fBTcl_GetStringFromObj\fR.

It parses the string to obtain an integer and,

if this succeeds,

stores the integer in \fIobjPtr\fR's internal representation

and sets \fIobjPtr\fR's \fItypePtr\fR member to point to the integer type's

Tcl_ObjType structure.

.PP

The \fIupdateStringProc\fR member contains the address of a function

called to create a valid string representation

from an object's internal representation.

.CS

typedef void (Tcl_UpdateStringProc) (Tcl_Obj *\fIobjPtr\fR);

.CE

\fIobjPtr\fR's \fIbytes\fR member is always NULL when it is called.

It must always set \fIbytes\fR non-NULL before returning.

We require the string representation's byte array

to have a null after the last byte, at offset \fIlength\fR;

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 \fBTcl_Alloc\fR.

Note that \fIupdateStringProc\fRs must allocate

enough storage for the string's bytes and the terminating null byte.

The \fIupdateStringProc\fR for Tcl's builtin list type, for example,

builds an array of strings for each element object

and then calls \fBTcl_Merge\fR

to construct a string with proper Tcl list structure.

It stores this string as the list object's string representation.

.PP

The \fIdupIntRepProc\fR member contains the address of a function

called to copy an internal representation from one object to another.

.CS

typedef void (Tcl_DupInternalRepProc) (Tcl_Obj *\fIsrcPtr\fR, Tcl_Obj *\fIdupPtr\fR);

.CE

\fIdupPtr\fR's internal representation is made a copy of \fIsrcPtr\fR's

internal representation.

Before the call,

\fIsrcPtr\fR's internal representation is valid and \fIdupPtr\fR's is not.

\fIsrcPtr\fR's object type determines what

copying its internal representation means.

For example, the \fIdupIntRepProc\fR for the Tcl integer type

simply copies an integer.

The builtin list type's \fIdupIntRepProc\fR

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).

.PP

The \fIfreeIntRepProc\fR member contains the address of a function

that is called when an object is freed.

.CS

typedef void (Tcl_FreeInternalRepProc) (Tcl_Obj *\fIobjPtr\fR);

.CE

The \fIfreeIntRepProc\fR 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 \fIinternalRep.otherValuePtr\fR

that points to an array of pointers to each element in the list.

The list type's \fIfreeIntRepProc\fR 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 \fIfreeIntRepProc\fR member can be set to NULL

to indicate that the internal representation does not require freeing.

.SH "SEE ALSO"

Tcl_NewObj, Tcl_DecrRefCount, Tcl_IncrRefCount

.SH KEYWORDS

internal representation, object, object type, string representation, type conversion