* GOOPS Error Handling::
* GOOPS Object Miscellany::
* The Metaobject Protocol::
-* Class Options::
* Redefining a Class::
* Changing the Class of an Instance::
@end menu
oriented systems. Each @var{slot-description} gives the name of a slot
and optionally some ``properties'' of this slot; for example its initial
value, the name of a function which will access its value, and so on.
-Slot descriptions and inheritance are discussed more below. For class
-options, see @ref{Class Options}.
+Class options, slot descriptions and inheritance are discussed more
+below.
@cindex slot
@deffn syntax define-class name (super @dots{}) slot-definition @dots{} . options
superclass of @code{<real>}, and @code{<real>} is the superclass of
@code{<integer>}.}
-The possible slot and class options are described in the following
-sections.
+Slot options are described in the next section. The possible class
+options are as follows.
+
+@deffn {class option} #:metaclass metaclass
+The @code{#:metaclass} class option specifies the metaclass of the class
+being defined. @var{metaclass} must be a class that inherits from
+@code{<class>}. For the use of metaclasses, see @ref{Metaobjects and
+the Metaobject Protocol} and @ref{Metaclasses}.
+
+If the @code{#:metaclass} option is absent, GOOPS reuses or constructs a
+metaclass for the new class by calling @code{ensure-metaclass}
+(@pxref{Class Definition Protocol,, ensure-metaclass}).
+@end deffn
+
+@deffn {class option} #:name name
+The @code{#:name} class option specifies the new class's name. This
+name is used to identify the class whenever related objects - the class
+itself, its instances and its subclasses - are printed.
+
+If the @code{#:name} option is absent, GOOPS uses the first argument to
+@code{define-class} as the class name.
+@end deffn
@node Instance Creation
In addition to the cases mentioned, you can of course define
@code{write} and @code{display} methods for your own classes, to
-customize how they are printed.
+customize how instances of those classes are printed.
@node The Metaobject Protocol
* Instance Creation Protocol::
* Class Definition Protocol::
* Customizing Class Definition::
-* Class Redefinition::
* Method Definition::
* Method Definition Internals::
* Generic Function Internals::
@item
@code{compute-getter-method @var{class} @var{gns}} (generic)
-@code{initialize} calls @code{compute-getter-method} for each of the class's
-slots (as determined by @code{compute-slots}) that includes a
+@code{initialize} calls @code{compute-getter-method} for each of the
+class's slots (as determined by @code{compute-slots}) that includes a
@code{#:getter} or @code{#:accessor} slot option. @var{gns} is the
-element of the @var{class} metaobject's @code{getters-n-setters} slot that
-specifies how the slot in question is referenced and set, as described
-above under @code{compute-get-n-set}. The applied method should create
-and return a method that is specialized for instances of type @var{class}
-and uses the get closure to retrieve the slot's value. [ *fixme Need
-to insert something here about checking that the value is not unbound. ]
+element of the @var{class} metaobject's @code{getters-n-setters} slot
+that specifies how the slot in question is referenced and set, as
+described above under @code{compute-get-n-set}. The applied method
+should create and return a method that is specialized for instances of
+type @var{class} and uses the get closure to retrieve the slot's value.
@code{initialize} uses @code{add-method!} to add the returned method to
the generic function named by the slot definition's @code{#:getter} or
@code{#:accessor} option.
and/or after calling @code{(next-method)} for the standard behaviour.
-@node Class Redefinition
-@subsection Class Redefinition
-
-@itemize @bullet
-
-@item
-@code{class-redefinition @var{old-class} @var{new-class}} (generic)
-
-@code{define-class} calls @code{class-redefinition} if the variable
-specified by its first argument already held a GOOPS class definition.
-@var{old-class} and @var{new-class} are the old and new class metaobjects.
-The applied method should perform whatever is necessary to handle the
-redefinition, and should return the class metaobject that is to be bound
-to @code{define-class}'s variable. The default class redefinition
-protocol is described in @ref{Class Redefinition}.
-@end itemize
-
-The default @code{class-redefinition} method, specialized for classes
-with the default metaclass @code{<class>}, has the following internal
-protocol.
-
-@code{class-redefinition (@var{old <class>}) (@var{new <class>})}
-(method)
-
-@itemize @bullet
-@item
-@code{remove-class-accessors! @var{old}} (generic)
-
-@item
-@code{update-direct-method! @var{method} @var{old} @var{new}} (generic)
-
-@item
-@code{update-direct-subclass! @var{subclass} @var{old} @var{new}} (generic)
-@end itemize
-
-This protocol cleans up things that the definition of the old class
-once changed and modifies things to work with the new class.
-
-The default @code{remove-class-accessors!} method removes the
-accessor methods of the old class from all classes which they
-specialize.
-
-The default @code{update-direct-method!} method substitutes the new
-class for the old in all methods specialized to the old class.
-
-The default @code{update-direct-subclass!} method invokes
-@code{class-redefinition} recursively to handle the redefinition of
-subclasses.
-
-When a class is redefined, any existing instance of the redefined class
-will be modified for the new class definition before the next time that
-any of the instance's slot is referenced or set. GOOPS modifies each
-instance by calling the generic function @code{change-class}.
-
-The default @code{change-class} method copies slot values from the old
-to the modified instance, and initializes new slots, as described in
-@ref{Changing the Class of an Instance}. After doing so, it makes a
-generic function invocation that can be used to customize the instance
-update algorithm.
-
-@code{change-class (@var{old-instance <object>}) (@var{new <class>})} (method)
-
-@itemize @bullet
-@item
-@code{update-instance-for-different-class @var{old-instance} @var{new-instance}} (generic)
-
-@code{change-class} invokes @code{update-instance-for-different-class}
-as the last thing that it does before returning. The applied method can
-make any further adjustments to @var{new-instance} that are required to
-complete or modify the change of class. The return value from the
-applied method is ignored.
-
-The default @code{update-instance-for-different-class} method does
-nothing.
-@end itemize
-
@node Method Definition
@subsection Method Definition
@itemize @bullet
@item
@code{add-method! @var{target} @var{method}} (generic)
+@end itemize
+@noindent
@code{define-method} invokes the @code{add-method!} generic function to
handle adding the new method to a variety of possible targets. GOOPS
includes methods to handle @var{target} as
By defining further methods for @code{add-method!}, you can
theoretically handle adding methods to further types of target.
-@end itemize
+
@node Method Definition Internals
@subsection Method Definition Internals
-@code{define-method}
+@code{define-method}:
@itemize @bullet
@item
define-method}).
@end deffn
-@code{method}
+@noindent
+@code{method}:
@itemize @bullet
@item
function parameters when this method is invoked.
@end deffn
+@noindent
@code{make-method} is a simple wrapper around @code{make} with metaclass
@code{<method>}.
@node Generic Function Invocation
@subsection Generic Function Invocation
-[ *fixme* Description required here. ]
+There is a detailed and customizable protocol involved in the process of
+invoking a generic function --- i.e., in the process of deciding which
+of the generic function's methods are applicable to the current
+arguments, and which one of those to apply. Here is a summary diagram
+of the generic functions involved.
-@code{apply-generic}
+@noindent
+@code{apply-generic} (generic)
@itemize @bullet
@item
-@code{no-method}
-
-@item
-@code{compute-applicable-methods}
+@code{no-method} (generic)
@item
-@code{sort-applicable-methods}
+@code{compute-applicable-methods} (generic)
@item
-@code{apply-methods}
+@code{sort-applicable-methods} (generic)
+@itemize @bullet
@item
-@code{no-applicable-method}
+@code{method-more-specific?} (generic)
@end itemize
-@code{sort-applicable-methods}
+@item
+@code{apply-methods} (generic)
@itemize @bullet
@item
-@code{method-more-specific?}
-@end itemize
-
-@code{apply-methods}
+@code{apply-method} (generic)
-@itemize @bullet
@item
-@code{apply-method}
+@code{no-next-method} (generic)
@end itemize
-@code{next-method}
-
-@itemize @bullet
@item
-@code{no-next-method}
+@code{no-applicable-method}
@end itemize
-
-@node Class Options
-@section Class Options
-
-@deffn {class option} #:metaclass metaclass
-The @code{#:metaclass} class option specifies the metaclass of the class
-being defined. @var{metaclass} must be a class that inherits from
-@code{<class>}. For the use of metaclasses, see @ref{Metaobjects and
-the Metaobject Protocol} and @ref{Metaclasses}.
-
-If the @code{#:metaclass} option is absent, GOOPS reuses or constructs a
-metaclass for the new class by calling @code{ensure-metaclass}
-(@pxref{Class Definition Protocol,, ensure-metaclass}).
-@end deffn
-
-@deffn {class option} #:name name
-The @code{#:name} class option specifies the new class's name. This
-name is used to identify the class whenever related objects - the class
-itself, its instances and its subclasses - are printed.
-
-If the @code{#:name} option is absent, GOOPS uses the first argument to
-@code{define-class} as the class name.
-@end deffn
+We do not yet have full documentation for these. Please refer to the
+code (@file{oop/goops.scm}) for details.
@node Redefining a Class
@node Customizing Class Redefinition
@subsection Customizing Class Redefinition
-When @code{define-class} notices that a class is being redefined,
-it constructs the new class metaobject as usual, and then invokes the
+When @code{define-class} notices that a class is being redefined, it
+constructs the new class metaobject as usual, then invokes the
@code{class-redefinition} generic function with the old and new classes
as arguments. Therefore, if the old or new classes have metaclasses
other than the default @code{<class>}, class redefinition behaviour can
for the new class definition.
@end deffn
+The default @code{class-redefinition} method, for classes with the
+default metaclass @code{<class>}, calls the following generic functions,
+which could of course be individually customized.
+
+@deffn generic remove-class-accessors! old
+The default @code{remove-class-accessors!} method removes the accessor
+methods of the old class from all classes which they specialize.
+@end deffn
+
+@deffn generic update-direct-method! method old new
+The default @code{update-direct-method!} method substitutes the new
+class for the old in all methods specialized to the old class.
+@end deffn
+
+@deffn generic update-direct-subclass! subclass old new
+The default @code{update-direct-subclass!} method invokes
+@code{class-redefinition} recursively to handle the redefinition of
+subclasses.
+@end deffn
+
An alternative class redefinition strategy could be to leave all
existing instances as instances of the old class, but accepting that the
old class is now ``nameless'', since its name has been taken over by the
When customization can be as easy as this, aren't you glad that GOOPS
implements the far more difficult strategy as its default!
-Finally, note that, if @code{class-redefinition} itself is not customized,
-the default @code{class-redefinition} method invokes three further
-generic functions that could be individually customized:
-
-@itemize @bullet
-@item
-(remove-class-accessors! @var{old-class})
-
-@item
-(update-direct-method! @var{method} @var{old-class} @var{new-class})
-
-@item
-(update-direct-subclass! @var{subclass} @var{old-class} @var{new-class})
-@end itemize
-
-and the default methods for these generic functions invoke further
-generic functions, and so on@dots{} The detailed protocol for all of these
-is described in @ref{MOP Specification}.
@node Changing the Class of an Instance
@section Changing the Class of an Instance
-You can change the class of an existing instance by invoking the
-generic function @code{change-class} with two arguments: the instance
-and the new class.
+When a class is redefined, any existing instance of the redefined class
+will be modified for the new class definition before the next time that
+any of the instance's slots is referenced or set. GOOPS modifies each
+instance by calling the generic function @code{change-class}.
-@deffn generic change-class
-@end deffn
+More generally, you can change the class of an existing instance at any
+time by invoking the generic function @code{change-class} with two
+arguments: the instance and the new class.
The default method for @code{change-class} decides how to implement the
change of class by looking at the slot definitions for the instance's
using the corresponding slot definition's init function (@pxref{Classes,,
slot-init-function}).
+@deffn generic change-class instance new-class
+@end deffn
+
@deffn {method} change-class (obj <object>) (new <class>)
Modify instance @var{obj} to make it an instance of class @var{new}.
init functions.
@end deffn
+The default @code{change-class} method also invokes another generic
+function, @code{update-instance-for-different-class}, as the last thing
+that it does before returning. The applied
+@code{update-instance-for-different-class} method can make any further
+adjustments to @var{new-instance} that are required to complete or
+modify the change of class. The return value from the applied method is
+ignored.
+
+@deffn generic update-instance-for-different-class old-instance new-instance
+A generic function that can be customized to put finishing touches to an
+instance whose class has just been changed. The default
+@code{update-instance-for-different-class} method does nothing.
+@end deffn
+
Customized change of class behaviour can be implemented by defining
@code{change-class} methods that are specialized either by the class
of the instances to be modified or by the metaclass of the new class.
-
-When a class is redefined (@pxref{Redefining a Class}), and the default
-class redefinition behaviour is not overridden, GOOPS (eventually)
-invokes the @code{change-class} generic function for each existing
-instance of the redefined class.
HCoop / bpt / guile.git / blobdiff