1. Module (chicken locative)
    1. make-locative
    2. make-weak-locative
    3. locative?
    4. locative-ref
    5. locative-set!
    6. locative->object
    7. locative-index

Module (chicken locative)

A locative is an object that points to an element of a containing object, much like a pointer in low-level, imperative programming languages like C. The element can be accessed and changed indirectly, by performing access or change operations on the locative. The container object can be computed by calling the locative->object procedure.

Locatives may be passed to foreign procedures that expect pointer arguments.

The following procedures are provided by the (chicken locative) module.

make-locative

[procedure] (make-locative OBJ [INDEX])

Creates a locative that refers to the element of the non-immediate object OBJ at position INDEX. OBJ may be a vector, pair, string, bytevector, SRFI-4 number-vector, or record structure. INDEX should be a fixnum. INDEX defaults to 0. Note that INDEX designates a character-position for string objects, not a byte offset.

make-weak-locative

[procedure] (make-weak-locative OBJ [INDEX])

Creates a weak locative. Even though the locative refers to an element of a container object, the container object will still be reclaimed by garbage collection if no other references to it exist.

locative?

[procedure] (locative? X)

Returns #t if X is a locative, or #f otherwise.

locative-ref

[procedure] (locative-ref LOC)

Returns the element to which the locative LOC refers. If the containing object has been reclaimed by garbage collection, an error is signalled.

(locative-ref (make-locative "abc" 1)) ==> #\b

locative-set!

[procedure] (locative-set! LOC X)
[procedure] (set! (locative-ref LOC) X)

Changes the element to which the locative LOC refers to X. If the containing object has been reclaimed by garbage collection, an error is signalled.

locative->object

[procedure] (locative->object LOC)

Returns the object that contains the element referred to by LOC or #f if the container has been reclaimed by garbage collection.

(locative->object (make-locative "abc" 1)) ==> "abc"

locative-index

[procedure] (locative-index LOC)

Returns the index (position) of the element that LOC refers to.

(locative-index (make-locative "abcde" 3)) ==> 3

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