fill-pointer

(fill-pointer vector)

Returns the fill pointer of a vector created with make-array :fill-pointer. The fill pointer is the vector's effective length: length and printing stop at it, while aref can still reach the full backing storage. It is a setf place, so (setf (fill-pointer v) n) moves it to any position between 0 and the vector's total size. An array without a fill pointer -- a string literal, a simple or packed vector, a rank-2 array -- signals a type-error whose expected type is (and vector (satisfies array-has-fill-pointer-p)): FILL-POINTER: The value "abc" is not of type (AND VECTOR (SATISFIES ARRAY-HAS-FILL-POINTER-P)) (test with array-has-fill-pointer-p first). A vector that is no array at all signals a type-error whose expected type is array: FILL-POINTER: The value 5 is not of type ARRAY. On the wasm-GC backends both need a program with a catching form; without one they trap. vector-push, vector-push-extend and vector-pop report both the same way under their own names, a store as (SETF FILL-POINTER), and adjust-array and the other accessors of an array's shape report the second. A stored value that is no integer between 0 and the vector's total size signals a type-error whose expected type is (integer 0 size): (SETF FILL-POINTER): The value 9 is not of type (INTEGER 0 5).