《通链参考手册》


Macro DEFGENERIC

●语法设定:

defgeneric function-name gf-lambda-list [[option | {method-description}*]]

=> new-generic

option::= (:argument-precedence-order parameter-name+) | 
          (declare gf-declaration+) | 
          (:documentation gf-documentation) | 
          (:method-combination method-combination method-combination-argument*) | 
          (:generic-function-class generic-function-class) | 
          (:method-class method-class) 
method-description::= (:method method-qualifier* specialized-lambda-list [[declaration* | documentation]] form*) 

●参数和值:

function-name---a function name.

generic-function-class---a non-nil symbol naming a class.

gf-declaration---an optimize declaration specifier; other declaration specifiers are not permitted.

gf-documentation---a string; not evaluated.

gf-lambda-list---a generic function lambda list.

method-class---a non-nil symbol naming a class.

method-combination-argument---an object.

method-combination-name---a symbol naming a method combination type.

method-qualifiers, specialized-lambda-list, declarations, documentation, forms---as per defmethod.

new-generic---the generic function object.

parameter-name---a symbol that names a required parameter in the lambda-list. (If the :argument-precedence-order option is specified, each required parameter in the lambda-list must be used exactly once as a parameter-name.)

●详情:

The macro defgeneric is used to define a generic function or to specify options and declarations that pertain to a generic function as a whole.

If function-name is a list it must be of the form (setf symbol). If (fboundp function-name) is false, a new generic function is created. If (fdefinition function-name) is a generic function, that generic function is modified. If function-name names an ordinary function, a macro, or a special operator, an error is signaled.

The effect of the defgeneric macro is as if the following three steps were performed: first, methods defined by previous defgeneric forms are removed; second, ensure-generic-function is called; and finally, methods specified by the current defgeneric form are added to the generic function.

Each method-description defines a method on the generic function. The lambda list of each method must be congruent with the lambda list specified by the gf-lambda-list option. If no method descriptions are specified and a generic function of the same name does not already exist, a generic function with no methods is created.

The gf-lambda-list argument of defgeneric specifies the shape of lambda lists for the methods on this generic function. All methods on the resulting generic function must have lambda lists that are congruent with this shape. If a defgeneric form is evaluated and some methods for that generic function have lambda lists that are not congruent with that given in the defgeneric form, an error is signaled. For further details on method congruence, see Section 7.6.4 (Congruent Lambda-lists for all Methods of a Generic Function).

The generic function passes to the method all the argument values passed to it, and only those; default values are not supported. Note that optional and keyword arguments in method definitions, however, can have default initial value forms and can use supplied-p parameters.

The following options are provided. Except as otherwise noted, a given option may occur only once.

The method-description arguments define methods that will be associated with the generic function. The method-qualifier and specialized-lambda-list arguments in a method description are the same as for defmethod.

The form arguments specify the method body. The body of the method is enclosed in an implicit block. If function-name is a symbol, this block bears the same name as the generic function. If function-name is a list of the form (setf symbol), the name of the block is symbol.

Implementations can extend defgeneric to include other options. It is required that an implementation signal an error if it observes an option that is not implemented locally.

defgeneric is not required to perform any compile-time side effects. In particular, the methods are not installed for invocation during compilation. An implementation may choose to store information about the generic function for the purposes of compile-time error-checking (such as checking the number of arguments on calls, or noting that a definition for the function name has been seen).

●例子:

●受制于: 无。

●例外情况:

If function-name names an ordinary function, a macro, or a special operator, an error of type program-error is signaled.

Each required argument, as specified in the gf-lambda-list argument, must be included exactly once as a parameter-name, or an error of type program-error is signaled.

The lambda list of each method specified by a method-description must be congruent with the lambda list specified by the gf-lambda-list option, or an error of type error is signaled.

If a defgeneric form is evaluated and some methods for that generic function have lambda lists that are not congruent with that given in the defgeneric form, an error of type error is signaled.

A given option may occur only once, or an error of type program-error is signaled.

If function-name specifies an existing generic function that has a different value for the :generic-function-class argument and the new generic function class is compatible with the old, change-class is called to change the class of the generic function; otherwise an error of type error is signaled.

Implementations can extend defgeneric to include other options. It is required that an implementation signal an error of type program-error if it observes an option that is not implemented locally.

●更多信息:

defmethod, documentation, ensure-generic-function, generic-function, Section 7.6.4 (Congruent Lambda-lists for all Methods of a Generic Function)

●说明: 无。


X3J13设计清单非标准部分,可查下面章节:


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