vector-set! - modify an element of a vector
(import (rnrs)) ;R6RS
(import (rnrs base)) ;R6RS
(import (scheme r5rs)) ;R7RS
(import (scheme base)) ;R7RS
(vector-set! vector k obj)
Stores obj in element k of vector.
Constants in the source code are not supposed to be modified by the program, but
programs may still be able to do so. A compiler that creates executable files
can place the constants in read-only pages, where the processor will
automatically report attempts to mutate them. Interpreters and online
compilers normally skip this step and tend to not detect mutation of
constants. Implementations can also mark a vector as immutable using various
strategies like special memory ranges, a special immutable vector tag or an
immutable bit next to the length field.
Implementations may also do different things in different modes,
so just testing at the REPL is not a reliable method to check if constants
are always mutable or not in a particular implementation.
- R6RS
- Returns unspecified values.
- R7RS
- Returns an unspecified value.
(let ((vec (vector 0 '(2 2 2 2) "Anna")))
(vector-set! vec 1 '("Sue" "Sue"))
vec)
=> #(0 ("Sue" "Sue") "Anna")
;; This example shows mutation of a constant vector. Constants are
;; allowed to be immutable, but implementations do not always check
;; this. It should raise an &assertion exception.
(vector-set! '#(0 1 2) 1 "doe")
=> unspecified
; should raise &assertion exception
The specification of vectors does not actually require constant access time, but
in practice they are always implemented as flat arrays. Therefore this
procedure is used in algorithms that perform random-access operations on
arrays. Such algorithms would not have the same time complexity if lists were
used instead.
This procedure works the same everywhere.
This procedure can raise exceptions with the following condition types:
- &assertion (R6RS)
- The wrong number of arguments was passed or an argument was outside its
domain. In particular, vector should be a mutable vector, and
k must be an exact nonnegative integer less than the length of
vector.
- R7RS
- The assertions described above are errors. Implementations may signal an
error, extend the procedure's domain of definition to include such
arguments, or fail catastrophically.
R4RS, IEEE Scheme, R5RS, R6RS, R7RS
This procedure first appeared in R2RS, where the vector notation was optional.
Programs should not modify constants.