8. Predicates and Utilities
Now that we know how to create classes, access slots, and define
methods, it might be useful to verify that everything is doing ok. To
help with this a plethora of predicates have been created.
- Function: class-v class
- Return a vector with all the class's important parts in it. This vector
is not a copy. Changing this vector changes the class. The CLOS method
find-class will have the same effect.
- Function: find-class symbol &optional errorp
- CLOS function. In EIEIO it returns the vector definition of the class.
If there is no class,
nil is returned if errorp is
- Function: class-p class
- Return non-
nil if class is a class type.
- Function: object-p obj
- Return non-
nil if obj is an object.
- Function: slot-exists-p obj-or-class slot
- Return Non-
nil if obj-or-class contains slot in its class.
- Function: slot-boundp object slot
nil if OBJECT's SLOT is bound.
Setting a slot's value makes it bound. Calling slot-makeunbound will
make a slot unbound.
OBJECT can be an instance or a class.
- Function: class-name class
- Return a string of the form #<class myclassname> which should look
similar to other lisp objects like buffers and processes. Printing a
class results only in a symbol.
- Function: class-option class option
- Return the value in CLASS of a given OPTION.
(class-option eieio-default-superclass :documentation)
Will fetch the documentation string for
- Function: class-constructor class
- Return a symbol used as a constructor for class. This way you can
make an object of a passed in class without knowing what it is. This is
not a part of CLOS.
- Function: object-name obj
- Return a string of the form #<object-class myobjname> for obj.
This should look like lisp symbols from other parts of emacs such as
buffers and processes, and is shorter and cleaner than printing the
object's vector. It is more useful to use
object-print to get
and object's print form, as this allows the object to add extra display
information into the symbol.
- Function: object-class obj
- Returns the class symbol from obj.
- Function: class-of obj
- CLOS symbol which does the same thing as
- Function: object-class-fast obj
- Same as
object-class except this is a macro, and no
type-checking is performed.
- Function: object-class-name obj
- Returns the symbol of obj's class.
- Function: class-parents class
- Returns the direct parents class of class. Returns
it is a superclass.
- Function: class-parents-fast class
- Just like
class-parent except it is a macro and no type checking
- Function: class-parent class
- Deprecated function which returns the first parent of class.
- Function: class-children class
- Return the list of classes inheriting from class.
- Function: class-children-fast class
- Just like
class-children, but with no checks.
- Function: same-class-p obj class
t if obj's class is the same as class.
- Function: same-class-fast-p obj class
- Same as
same-class-p except this is a macro and no type checking
- Function: object-of-class-p obj class
t if obj inherits anything from class. This
is different from
same-class-p because it checks for inheritance.
- Function: child-of-class-p child class
t if child is a subclass of class.
- Function: generic-p method-symbol
method-symbol is a generic function, as
opposed to a regular emacs list function.
It is also important to note, that for every created class, a two
predicates are created for it. Thus in our example, the function
data-object-p is created, and return
t if passed an object
of the appropriate type. Also, the function
is created which returns
t if the object passed to it is of a
type which inherits from
This document was generated
by XEmacs Webmaster on October, 2 2007