Clojure: creating new instance from String class name

Question

In Clojure, given a class name as a string, I need to create a new instance of the class. In other words, how would I implement new-instance-from-class-name in

(def my-class-name "org.myorg.pkg.Foo")
; calls constructor of org.myorg.pkg.Foo with arguments 1, 2 and 3
(new-instance-from-class-name  my-class-name 1 2 3) 

I am looking for a solution more elegant than

• calling the Java newInstance method on a constructor from the class
• using eval, load-string, ...

In practice, I will be using it on classes created using defrecord. So if there is any special syntax for that scenario, I would be quite interested.

Answer 1

Since 'new' is a special form, I'm not sure there you can do this without a macro. Here is a way to do it using a macro:

user=> (defmacro str-new [s & args] `(new ~(symbol s) ~@args))
#'user/str-new
user=> (str-new "String" "LOL")
"LOL"

Check out Michal's comment on the limitations of this macro.

Answer 2

Here is a technique for extending defrecord to automatically create well-named constructor functions to construct record instances (either new or based on an existing record).

http://david-mcneil.com/post/765563763/enhanced-clojure-records