Common Lisp the Language, 2nd Edition
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The
generic function shared-initialize is used to fill the slots
of an instance using initialization arguments and :initform
forms when an instance is created, when an instance is re-initialized,
when an instance is updated to conform to a redefined class, and when
an instance is updated to conform to a different class. It uses
standard method combination. It takes the following arguments: the
instance to be initialized, a specification of a set of names of slots
accessible in that instance, and any number of initialization
arguments. The arguments after the first two must form an initialization
argument list.
The second argument to shared-initialize may be one of the following:
- It can be a list of slot names, which specifies
the set of those slot names.
- It can be nil, which specifies the empty set of
slot names.
- It can be the symbol t, which specifies the set of
all of the slots.
There is a system-supplied primary method for
shared-initialize whose first parameter specializer is the class
standard-object. This method behaves as follows on each slot,
whether shared or local:
- If an initialization argument in the initialization
argument list specifies a value for that slot, that value is stored
into the slot, even if a value has already been stored in the slot
before the method is run. The affected slots are independent of which
slots are indicated by the second argument to shared-initialize.
- Any slots indicated by the second argument that are still
unbound at this point are initialized according to their
:initform forms. For any such slot that has an :initform form,
that form is evaluated in the lexical environment of its defining
defclass form and the result is stored into the slot. For example,
if a :before method stores a value in the slot, the
:initform form will not be used to supply a value for the slot. If
the second argument specifies a name that does not correspond to any
slots accessible in the instance, the results are unspecified.
- The rules mentioned in section 28.1.9.4 are obeyed.
The generic function shared-initialize is called by the
system-supplied primary methods for the generic functions
initialize-instance,
reinitialize-instance,
update-instance-for-different-class, and
update-instance-for-redefined-class.
Thus methods can be written for
shared-initialize to specify actions that should be taken in all of
these contexts.
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