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(elisp)Vectors

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Vectors
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   Arrays in Lisp, like arrays in most languages, are blocks of memory
whose elements can be accessed in constant time.  A "vector" is a
general-purpose array of specified length; its elements can be any Lisp
objects.  (By contrast, a string can hold only characters as elements.)
Vectors in Emacs are used for obarrays (vectors of symbols), and as part
of keymaps (vectors of commands).  They are also used internally as part
of the representation of a byte-compiled function; if you print such a
function, you will see a vector in it.

   In Emacs Lisp, the indices of the elements of a vector start from
zero and count up from there.

   Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols `a', `b' and `a' is
printed as `[a b a]'.  You can write vectors in the same way in Lisp
input.

   A vector, like a string or a number, is considered a constant for
evaluation: the result of evaluating it is the same vector.  This does
not evaluate or even examine the elements of the vector.  Note:
Self-Evaluating Forms.

   Here are examples illustrating these principles:

     (setq avector [1 two '(three) "four" [five]])
          => [1 two (quote (three)) "four" [five]]
     (eval avector)
          => [1 two (quote (three)) "four" [five]]
     (eq avector (eval avector))
          => t