vector-of vs. vector in Clojure

Question

When would I use vector-of to create a vector, instead of the vector function. Is the guideline to use vector most of the time and only for performance reason switch to vector-of?

I could not find good info on when to use vector-of.

Answer 1

vector-of is used for creating a vector of a single primitive type, :int, :long, :float, :double, :byte, :short, :char, or :boolean. It doesn't allow other types as it stores the values unboxed internally. So, if your vector need to include other types than those primitive types, you cannot use vector-of. But if you are sure that the vector will have data of a single primitive type, you can use vector-of for better performance.

user=> (vector-of :int 1 2 3 4 5)
[1 2 3 4 5]
user=> (vector-of :double 1.0 2.0)
[1.0 2.0]
user=> (vector-of :string "hello" "world")
Execution error (IllegalArgumentException) at user/eval5 (REPL:1).
Unrecognized type :string

As you can see, you should specify primitive type as an argument.

vector can be used to create a vector of any type.

user=> (vector 1 2.0 "hello")
[1 2.0 "hello"]

You can put any type when you use vector.

Also, there's another function vec, which is used for creating a new vector containing the contents of coll.

user=> (vec '(1 2 3 4 5))
[1 2 3 4 5]

Usually, you can get the basic information of a function/macro from the repl, like the following.

user=> (doc vector-of)
-------------------------
clojure.core/vector-of
([t] [t & elements])
  Creates a new vector of a single primitive type t, where t is one
  of :int :long :float :double :byte :short :char or :boolean. The
  resulting vector complies with the interface of vectors in general,
  but stores the values unboxed internally.

  Optionally takes one or more elements to populate the vector.

Reference:

• https://clojuredocs.org/clojure.core/vector-of
• https://clojuredocs.org/clojure.core/vector
• https://clojuredocs.org/clojure.core/vec

Answer 2

Nobody really ever uses vector-of. If you don't super care about performance, vector is fine, and if you do super care about performance you usually want a primitive array or some other java type. Honestly I would expect occasional weird snags when passing a vector-of to anything that expects an ordinary vector or sequence - maybe it works fine, but it's just such a rare thing to see that it wouldn't surprise me if it caused issues.