I could have sworn I had alength
working previously, but I don't quite know what I am doing wrong right now:
user=> (alength '(1 2 3))
IllegalArgumentException No matching method found: alength clojure.lang.Reflector.invokeMatchingMethod (Reflector.java:79)
user=> (alength [1 2 3])
IllegalArgumentException No matching method found: alength clojure.lang.Reflector.invokeMatchingMethod (Reflector.java:79)
user=> (doc alength)
-------------------------
clojure.core/alength
([array])
Returns the length of the Java array. Works on arrays of all
types.
nil
What should I be doing to get the length of a list/array in Clojure?
As the docstring says, alength
works on Java™ arrays, such as a String[]
or Integer[]
, which is definitely an incompatible type with Clojure lists or vectors, for which you want to use count
:
user=> (def x '(1 2 3))
#'user/x
user=> (def xa (to-array x))
#'user/xa
user=> (class x)
clojure.lang.PersistentList
user=> (class xa)
[Ljava.lang.Object;
user=> (alength xa)
3
user=> (alength x)
java.lang.IllegalArgumentException: No matching method found: alength (NO_SOURCE_FILE:0)
user=> (count x)
3
[Ljava.lang.Object;
is the weird way toString
is defined to output for native Object
arrays.