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A *vector* is a general-purpose array whose elements can be any
Lisp objects. (By contrast, the elements of a string can only be
characters. See Strings and Characters.) Vectors are used in
Emacs for many purposes: as key sequences (see Key Sequences), as
symbol-lookup tables (see Creating Symbols), as part of the
representation of a byte-compiled function (see Byte Compilation),
and more.

Like other arrays, vectors use zero-origin indexing: the first element has index 0.

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.
See Self-Evaluating Forms. Vectors written with square brackets
should not be modified via `aset`

or other destructive
operations. See Mutability.

Here are examples illustrating these principles:

(setq avector [1 two '(three) 'four' [five]]) ⇒ [1 two '(three) 'four' [five]] (eval avector) ⇒ [1 two '(three) 'four' [five]] (eq avector (eval avector)) ⇒ t