1Tcl_ObjType(3) Tcl Library Procedures Tcl_ObjType(3)
2______________________________________________________________________________
6
8 Tcl_RegisterObjType, Tcl_GetObjType, Tcl_AppendAllObjTypes, Tcl_Con‐
9 vertToType - manipulate Tcl value types
10
12 #include <tcl.h>
13 Tcl_RegisterObjType(typePtr)
15 const Tcl_ObjType *
17 Tcl_GetObjType(typeName)
18 int
20 Tcl_AppendAllObjTypes(interp, objPtr)
21 int
23 Tcl_ConvertToType(interp, objPtr, typePtr)
24
26 const Tcl_ObjType *typePtr (in) Points to the structure containing
27 information about the Tcl value
28 type. This storage must live for‐
29 ever, typically by being statically
30 allocated.
31 const char *typeName (in) The name of a Tcl value type that
33 Tcl_GetObjType should look up.
34 Tcl_Interp *interp (in) Interpreter to use for error report‐
36 ing.
37 Tcl_Obj *objPtr (in) For Tcl_AppendAllObjTypes, this
39 points to the value onto which it
40 appends the name of each value type
41 as a list element. For Tcl_Convert‐
42 ToType, this points to a value that
43 must have been the result of a pre‐
44 vious call to Tcl_NewObj.
45______________________________________________________________________________
46
49 The procedures in this man page manage Tcl value types (sometimes
50 referred to as object types or Tcl_ObjTypes for historical reasons).
51 They are used to register new value types, look up types, and force
52 conversions from one type to another.
53 Tcl_RegisterObjType registers a new Tcl value type in the table of all
55 value types that Tcl_GetObjType can look up by name. There are other
56 value types supported by Tcl as well, which Tcl chooses not to regis‐
57 ter. Extensions can likewise choose to register the value types they
58 create or not. The argument typePtr points to a Tcl_ObjType structure
59 that describes the new type by giving its name and by supplying point‐
60 ers to four procedures that implement the type. If the type table
61 already contains a type with the same name as in typePtr, it is
62 replaced with the new type. The Tcl_ObjType structure is described in
63 the section THE TCL_OBJTYPE STRUCTURE below.
64 Tcl_GetObjType returns a pointer to the registered Tcl_ObjType with
66 name typeName. It returns NULL if no type with that name is regis‐
67 tered.
68 Tcl_AppendAllObjTypes appends the name of each registered value type as
70 a list element onto the Tcl value referenced by objPtr. The return
71 value is TCL_OK unless there was an error converting objPtr to a list
72 value; in that case TCL_ERROR is returned.
73 Tcl_ConvertToType converts a value from one type to another if possi‐
75 ble. It creates a new internal representation for objPtr appropriate
76 for the target type typePtr and sets its typePtr member as determined
77 by calling the typePtr->setFromAnyProc routine. Any internal represen‐
78 tation for objPtr's old type is freed. If an error occurs during con‐
79 version, it returns TCL_ERROR and leaves an error message in the result
80 value for interp unless interp is NULL. Otherwise, it returns TCL_OK.
81 Passing a NULL interp allows this procedure to be used as a test
82 whether the conversion can be done (and in fact was done). │
83 In many cases, the typePtr->setFromAnyProc routine will set │
85 objPtr->typePtr to the argument value typePtr, but that is no longer │
86 guaranteed. The setFromAnyProc is free to set the internal representa‐ │
87 tion for objPtr to make use of another related Tcl_ObjType, if it sees │
88 fit.
89
91 Extension writers can define new value types by defining four proce‐
92 dures and initializing a Tcl_ObjType structure to describe the type.
93 Extension writers may also pass a pointer to their Tcl_ObjType struc‐
94 ture to Tcl_RegisterObjType if they wish to permit other extensions to
95 look up their Tcl_ObjType by name with the Tcl_GetObjType routine. The
96 Tcl_ObjType structure is defined as follows:
97 typedef struct Tcl_ObjType {
99 const char *name;
100 Tcl_FreeInternalRepProc *freeIntRepProc;
101 Tcl_DupInternalRepProc *dupIntRepProc;
102 Tcl_UpdateStringProc *updateStringProc;
103 Tcl_SetFromAnyProc *setFromAnyProc;
104 } Tcl_ObjType;
105 THE NAME FIELD
107 The name member describes the name of the type, e.g. int. When a type
108 is registered, this is the name used by callers of Tcl_GetObjType to
109 lookup the type. For unregistered types, the name field is primarily
110 of value for debugging. The remaining four members are pointers to
111 procedures called by the generic Tcl value code:
112 THE SETFROMANYPROC FIELD
114 The setFromAnyProc member contains the address of a function called to
115 create a valid internal representation from a value's string represen‐
116 tation.
117 typedef int Tcl_SetFromAnyProc(
119 Tcl_Interp *interp,
120 Tcl_Obj *objPtr);
121 If an internal representation cannot be created from the string, it
123 returns TCL_ERROR and puts a message describing the error in the result
124 value for interp unless interp is NULL. If setFromAnyProc is success‐
125 ful, it stores the new internal representation, sets objPtr's typePtr
126 member to point to the Tcl_ObjType struct corresponding to the new
127 internal representation, and returns TCL_OK. Before setting the new
128 internal representation, the setFromAnyProc must free any internal rep‐
129 resentation of objPtr's old type; it does this by calling the old
130 type's freeIntRepProc if it is not NULL.
131 As an example, the setFromAnyProc for the built-in Tcl list type gets
133 an up-to-date string representation for objPtr by calling Tcl_Get‐
134 StringFromObj. It parses the string to verify it is in a valid list
135 format and to obtain each element value in the list, and, if this suc‐
136 ceeds, stores the list elements in objPtr's internal representation and
137 sets objPtr's typePtr member to point to the list type's Tcl_ObjType
138 structure.
139 Do not release objPtr's old internal representation unless you replace
141 it with a new one or reset the typePtr member to NULL.
142 The setFromAnyProc member may be set to NULL, if the routines making
144 use of the internal representation have no need to derive that internal
145 representation from an arbitrary string value. However, in this case,
146 passing a pointer to the type to Tcl_ConvertToType will lead to a
147 panic, so to avoid this possibility, the type should not be registered.
148 THE UPDATESTRINGPROC FIELD
150 The updateStringProc member contains the address of a function called
151 to create a valid string representation from a value's internal repre‐
152 sentation.
153 typedef void Tcl_UpdateStringProc(
155 Tcl_Obj *objPtr);
156 objPtr's bytes member is always NULL when it is called. It must always
158 set bytes non-NULL before returning. We require the string representa‐
159 tion's byte array to have a null after the last byte, at offset length,
160 and to have no null bytes before that; this allows string representa‐
161 tions to be treated as conventional null character-terminated C
162 strings. These restrictions are easily met by using Tcl's internal UTF
163 encoding for the string representation, same as one would do for other
164 Tcl routines accepting string values as arguments. Storage for the
165 byte array must be allocated in the heap by Tcl_Alloc or ckalloc. Note
166 that updateStringProcs must allocate enough storage for the string's
167 bytes and the terminating null byte.
168 The updateStringProc for Tcl's built-in double type, for example, calls
170 Tcl_PrintDouble to write to a buffer of size TCL_DOUBLE_SPACE, then
171 allocates and copies the string representation to just enough space to
172 hold it. A pointer to the allocated space is stored in the bytes mem‐
173 ber.
174 The updateStringProc member may be set to NULL, if the routines making
176 use of the internal representation are written so that the string rep‐
177 resentation is never invalidated. Failure to meet this obligation will
178 lead to panics or crashes when Tcl_GetStringFromObj or other similar
179 routines ask for the string representation.
180 THE DUPINTREPPROC FIELD
182 The dupIntRepProc member contains the address of a function called to
183 copy an internal representation from one value to another.
184 typedef void Tcl_DupInternalRepProc(
186 Tcl_Obj *srcPtr,
187 Tcl_Obj *dupPtr);
188 dupPtr's internal representation is made a copy of srcPtr's internal
190 representation. Before the call, srcPtr's internal representation is
191 valid and dupPtr's is not. srcPtr's value type determines what copying
192 its internal representation means.
193 For example, the dupIntRepProc for the Tcl integer type simply copies
195 an integer. The built-in list type's dupIntRepProc uses a far more
196 sophisticated scheme to continue sharing storage as much as it reason‐
197 ably can.
198 THE FREEINTREPPROC FIELD
200 The freeIntRepProc member contains the address of a function that is
201 called when a value is freed.
202 typedef void Tcl_FreeInternalRepProc(
204 Tcl_Obj *objPtr);
205 The freeIntRepProc function can deallocate the storage for the value's
207 internal representation and do other type-specific processing necessary
208 when a value is freed.
209 For example, the list type's freeIntRepProc respects the storage shar‐
211 ing scheme established by the dupIntRepProc so that it only frees stor‐
212 age when the last value sharing it is being freed.
213 The freeIntRepProc member can be set to NULL to indicate that the
215 internal representation does not require freeing. The freeIntRepProc
216 implementation must not access the bytes member of the value, since Tcl
217 makes its own internal uses of that field during value deletion. The
218 defined tasks for the freeIntRepProc have no need to consult the bytes
219 member.
220
222 Tcl_NewObj(3), Tcl_DecrRefCount(3), Tcl_IncrRefCount(3)
223
225 internal representation, value, value type, string representation, type
226 conversion
227Tcl 8.0 Tcl_ObjType(3)