Given a method, the entity that declared it can be found using Tcl_MethodDeclarerClass which returns the class that the method is attached to (or NULL if the method is not attached to any class) and Tcl_MethodDeclarerObject which returns the object that the method is attached to (or NULL if the method is not attached to an object). The name of the method can be retrieved with Tcl_MethodName, whether the method is exported is retrieved with Tcl_MethodIsPublic, and whether the method is private is retrieved with Tcl_MethodIsPrivate. The type of the method can also be introspected upon to a limited degree; the function Tcl_MethodIsType returns whether a method is of a particular type, assigning the per-method clientData to the variable pointed to by clientDataPtr if (that is non-NULL) if the type is matched.
When the nameObj argument to Tcl_NewMethod is NULL, an unnamed method is created, which is used for constructors and destructors. Constructors should be installed into their class using the Tcl_ClassSetConstructor function, and destructors (which must not require any arguments) should be installed into their class using the Tcl_ClassSetDestructor function. Unnamed methods should not be used for any other purpose, and named methods should not be used as either constructors or destructors. Also note that a NULL methodTypePtr is used to provide internal signaling, and should not be used in client code.
The method that is being called can be retrieved from the context by using Tcl_ObjectContextMethod, and the object that caused the method to be invoked can be retrieved with Tcl_ObjectContextObject. The number of arguments that are to be skipped (e.g. the object name and method name in a normal method call) is read with Tcl_ObjectContextSkippedArgs, and the context can also report whether it is working as a filter for another method through Tcl_ObjectContextIsFiltering.
During the execution of a method, the method implementation may choose to invoke the stages of the method call chain that come after the current method implementation. This (the core of the next command) is done using Tcl_ObjectContextInvokeNext. Note that this function does not manipulate the call-frame stack, unlike the next command; if the method implementation has pushed one or more extra frames on the stack as part of its implementation, it is also responsible for temporarily popping those frames from the stack while the Tcl_ObjectContextInvokeNext function is executing. Note also that the method-call context is never deleted during the execution of this function.
typedef struct {
int version;
const char *name;
Tcl_MethodCallProc *callProc;
Tcl_MethodDeleteProc *deleteProc;
Tcl_CloneProc *cloneProc;
} Tcl_MethodType;
The version field allows for future expansion of the structure, and should always be declared equal to TCL_OO_METHOD_VERSION_CURRENT. The name field provides a human-readable name for the type, and is the value that is exposed via the info class methodtype and info object methodtype Tcl commands.
The callProc field gives a function that is called when the method is invoked; it must never be NULL.
The deleteProc field gives a function that is used to delete a particular method, and is called when the method is replaced or removed; if the field is NULL, it is assumed that the method's clientData needs no special action to delete.
The cloneProc field is either a function that is used to copy a method's clientData (as part of Tcl_CopyObjectInstance) or NULL to indicate that the clientData can just be copied directly.
typedef int Tcl_MethodCallProc(
void *clientData,
Tcl_Interp *interp,
Tcl_ObjectContext objectContext,
int objc,
Tcl_Obj *const *objv);
The clientData argument to a Tcl_MethodCallProc is the value that was given when the method was created, the interp is a place in which to execute scripts and access variables as well as being where to put the result of the method, and the objc and objv fields give the parameter objects to the method. The calling context of the method can be discovered through the objectContext argument, and the return value from a Tcl_MethodCallProc is any Tcl return code (e.g. TCL_OK, TCL_ERROR).
typedef void Tcl_MethodDeleteProc(
void *clientData);
The clientData argument to a Tcl_MethodDeleteProc will be the same as the value passed to the clientData argument to Tcl_NewMethod or Tcl_NewInstanceMethod when the method was created.
typedef int Tcl_CloneProc(
Tcl_Interp *interp,
void *oldClientData,
void **newClientDataPtr);
The interp argument gives a place to write an error message when the attempt to clone the object is to fail, in which case the clone procedure must also return TCL_ERROR; it should return TCL_OK otherwise. The oldClientData field to a Tcl_CloneProc gives the value from the method being copied from, and the newClientDataPtr field will point to a variable in which to write the value for the method being copied to.
The result of Tcl_MethodName is a value with a reference count of at least one. It should not be modified without first duplicating it (with Tcl_DuplicateObj).
The values in the first objc values of the objv argument to Tcl_ObjectContextInvokeNext are assumed to have a reference count of at least 1; the containing array is assumed to endure until the next method implementation (see next) returns. Be aware that methods may yield; if any post-call actions are desired (e.g., decrementing the reference count of values passed in here), they must be scheduled with Tcl_NRAddCallback.
The callProc of the Tcl_MethodType structure takes values of at least reference count 1 in its objv argument. It may add its own references, but must not decrement the reference count below that level; the caller of the method will decrement the reference count once the method returns properly (and the reference will be held if the method yields).