plucky (3) Tcl_ClassSetConstructor.3tcl.gz
NAME
Tcl_ClassSetConstructor, Tcl_ClassSetDestructor, Tcl_MethodDeclarerClass, Tcl_MethodDeclarerObject,
Tcl_MethodIsPublic, Tcl_MethodIsPrivate, Tcl_MethodIsType, Tcl_MethodName, Tcl_NewInstanceMethod,
Tcl_NewMethod, Tcl_ObjectContextInvokeNext, Tcl_ObjectContextIsFiltering, Tcl_ObjectContextMethod,
Tcl_ObjectContextObject, Tcl_ObjectContextSkippedArgs - manipulate methods and method-call contexts
SYNOPSIS
#include <tclOO.h>
Tcl_Method
Tcl_NewMethod(interp, class, nameObj, flags, methodTypePtr,
clientData)
Tcl_Method
Tcl_NewInstanceMethod(interp, object, nameObj, flags, methodTypePtr,
clientData)
Tcl_ClassSetConstructor(interp, class, method)
Tcl_ClassSetDestructor(interp, class, method)
Tcl_Class
Tcl_MethodDeclarerClass(method)
Tcl_Object
Tcl_MethodDeclarerObject(method)
Tcl_Obj *
Tcl_MethodName(method)
int │
Tcl_MethodIsPublic(method) │
int
Tcl_MethodIsPrivate(method)
int
Tcl_MethodIsType(method, methodTypePtr, clientDataPtr)
int
Tcl_ObjectContextInvokeNext(interp, context, objc, objv, skip)
int
Tcl_ObjectContextIsFiltering(context)
Tcl_Method
Tcl_ObjectContextMethod(context)
Tcl_Object
Tcl_ObjectContextObject(context)
Tcl_Size
Tcl_ObjectContextSkippedArgs(context)
ARGUMENTS
Tcl_Interp *interp (in/out) The interpreter holding the object or class to create or update a method
in.
Tcl_Object object (in) The object to create the method in.
Tcl_Class class (in) The class to create the method in.
Tcl_Obj *nameObj (in) The name of the method to create. Should not be NULL unless creating
constructors or destructors.
int flags (in) A flag saying (currently) what the visibility of the method is. The
supported public values of this flag are TCL_OO_METHOD_PUBLIC (which is
fixed at 1 for backward compatibility) for an exported method,
TCL_OO_METHOD_UNEXPORTED (which is fixed at 0 for backward compatibility)
for a non-exported method, and TCL_OO_METHOD_PRIVATE for a private method. │
Tcl_MethodType *methodTypePtr (in)
A description of the type of the method to create, or the type of method
to compare against.
void *clientData (in) A piece of data that is passed to the implementation of the method without
interpretation.
void **clientDataPtr (out) A pointer to a variable in which to write the clientData value supplied
when the method was created. If NULL, the clientData value will not be
retrieved.
Tcl_Method method (in) A reference to a method to query.
Tcl_ObjectContext context (in) A reference to a method-call context. Note that client code must not
retain a reference to a context.
Tcl_Size objc (in) The number of arguments to pass to the method implementation.
Tcl_Obj *const *objv (in) An array of arguments to pass to the method implementation.
Tcl_Size skip (in) The number of arguments passed to the method implementation that do not
represent "real" arguments.
________________________________________________________________________________________________________________
DESCRIPTION
A method is an operation carried out on an object that is associated with the object. Every method must
be attached to either an object or a class; methods attached to a class are associated with all instances
(direct and indirect) of that class.
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.
METHOD CREATION
Methods are created by Tcl_NewMethod and Tcl_NewInstanceMethod, which create a method attached to a class
or an object respectively. In both cases, the nameObj argument gives the name of the method to create,
the flags argument states whether the method should be exported initially or be marked as a private │
method, the methodTypePtr argument describes the implementation of the method (see the METHOD TYPES
section below) and the clientData argument gives some implementation-specific data that is passed on to
the implementation of the method when it is called.
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.
METHOD CALL CONTEXTS
When a method is called, a method-call context reference is passed in as one of the arguments to the
implementation function. This context can be inspected to provide information about the caller, but
should not be retained beyond the moment when the method call terminates.
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.
METHOD TYPES
The types of methods are described by a pointer to a Tcl_MethodType structure, which is defined as:
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.
TCL_METHODCALLPROC FUNCTION SIGNATURE
Functions matching this signature are called when the method is invoked.
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).
TCL_METHODDELETEPROC FUNCTION SIGNATURE
Functions matching this signature are used when a method is deleted, whether through a new method being
created or because the object or class is deleted.
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.
TCL_CLONEPROC FUNCTION SIGNATURE
Functions matching this signature are used to copy a method when the object or class is copied using
Tcl_CopyObjectInstance (or oo::copy).
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.
REFERENCE COUNT MANAGEMENT
The nameObj argument to Tcl_NewMethod and Tcl_NewInstanceMethod (when non-NULL) will have its reference
count incremented if there is no existing method with that name in that class/object.
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).
SEE ALSO
Class(3tcl), NRE(3tcl), oo::class(3tcl), oo::define(3tcl), oo::object(3tcl)
KEYWORDS
constructor, method, object