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====== Macro WITH-ACCESSORS ====== ====Syntax==== * with-accessors (//slot-entry''*''//) //instance-form// //declaration''*''// //form''*''// → //result''*''// <blockquote> slot-entry ::= (//variable-name// //accessor-name//) </blockquote> ====Arguments and Values==== * //variable-name// - a //[[CL:Glossary:variable name]]//; not evaluated. * //accessor-name// - a //[[CL:Glossary:function name]]//; not evaluated. * //instance-form// - a //[[CL:Glossary:form]]//; evaluated. * //declaration// - a **[[CL:Symbols:declare]]** //[[CL:Glossary:expression]]//; not evaluated. * //forms// - an //[[CL:Glossary:implicit progn]]//. * //results// - the //[[CL:Glossary:values]]// returned by the //forms//. ====Description==== Creates a lexical environment in which the slots specified by //slot-entry// are lexically available through their accessors as if they were variables. The macro **with-accessors** invokes the appropriate accessors to //access// the //[[CL:Glossary:slot|slots]]// specified by //slot-entry//. Both **[[CL:Macros:setf]]** and **[[CL:Special Operators:setq]]** can be used to set the value of the //[[CL:Glossary:slot]]//. ====Examples==== <blockquote> ([[CL:Macros:defclass]] thing () ((x :initarg :x :accessor thing-x) (y :initarg :y :accessor thing-y))) <r>#<STANDARD-CLASS THING 250020173> </r> ([[CL:Macros:defmethod]] ([[CL:Macros:setf]] thing-x) :before (new-x (thing thing)) ([[CL:Functions:format]] [[CL:Constant Variables:t]] "~&Changing X from ~D to ~D in ~S.~%" (thing-x thing) new-x thing)) <r>#<STANDARD-METHOD (SETF THING-X) :BEFORE (T THING) 28226194></r> ([[CL:Macros:defparameter]] *thing1* ([[CL:Functions:make-instance]] 'thing :x 1 :y 2)) <r>#<THING 43135676> </r> ([[CL:Macros:defparameter]] *thing2* ([[CL:Functions:make-instance]] 'thing :x 7 :y 8)) <r>#<THING 43147374> </r> (with-accessors ((x1 thing-x) (y1 thing-y)) *thing1* (with-accessors ((x2 thing-x) (y2 thing-y)) *thing2* ([[CL:Functions:list]] ([[CL:Functions:list]] x1 (thing-x *thing1*) y1 (thing-y *thing1*) x2 (thing-x *thing2*) y2 (thing-y *thing2*)) ([[CL:Macros:setf]] x1 ([[CL:Functions:math-add|+]] y1 x2)) ([[CL:Functions:list]] x1 (thing-x *thing1*) y1 (thing-y *thing1*) x2 (thing-x *thing2*) y2 (thing-y *thing2*)) ([[CL:Macros:setf]] (thing-x *thing2*) ([[CL:Functions:list]] x1)) ([[CL:Functions:list]] x1 (thing-x *thing1*) y1 (thing-y *thing1*) x2 (thing-x *thing2*) y2 (thing-y *thing2*))))) <o>Changing X from 1 to 9 in #<THING 43135676>. Changing X from 7 to (9) in #<THING 43147374>. </o> <r>((1 1 2 2 7 7 8 8) 9 (9 9 2 2 7 7 8 8) (9) (9 9 2 2 (9) (9) 8 8))</r> </blockquote> ====Affected By==== **[[CL:Macros:defclass]]** ====Exceptional Situations==== The consequences are undefined if any //accessor-name// is not the name of an accessor for the //instance//. ====See Also==== * **[[CL:Macros:with-slots|Macro WITH-SLOTS]]** * **[[CL:Special Operatoors:symbol-macrolet|Special Operator SYMBOL-MACROLET]]** ====Notes==== A **with-accessors** expression of the form: <blockquote> (with-accessors (//slot-entry<sub>1</sub>// ... //slot-entry<sub>n</sub>//) //instance-form// //form<sub>1</sub>// ... //form<sub>k</sub>//) </blockquote> expands into the equivalent of <blockquote> ([[CL:Special Operators:let]] ((in //instance-form//)) ([[CL:Special Operators:symbol-macrolet]] (//Q<sub>1</sub>// ... //Q<sub>n</sub>//) //form<sub>1</sub>// ... //form<sub>k</sub>//)) </blockquote> where Q<sub>i</sub> is: <blockquote> (//variable-name<sub>i</sub>// () (//accessor-name<sub>i</sub>// in)) </blockquote> \issue{DECLS-AND-DOC}