CODEWITHSUNDEEP
constructorclojure
AnnanFay
AnnanFay

Reputation: 9749

Calling apply with a defrecord constructor?

core=> (defrecord Puffball [id name])
core.Puffball
core=> (Puffball. 149 "Urist")
#core.Puffball{:id 149, :name "Urist"}
core=> (apply Puffball. [149 "Urist"])
CompilerException java.lang.RuntimeException: java.lang.ClassNotFoundException: Puffball., compiling:(NO_SOURCE_PATH:3)
core=> (apply Puffball [149 "Urist"])
ClassCastException java.lang.Class cannot be cast to clojure.lang.IFn  clojure.core/apply (core.clj:600)

How can I create puffballs from vectors?

Upvotes: 2

Views: 595

Answers (2)

Alex Taggart
Alex Taggart

Reputation: 7825

For those not on 1.3.x (or need such functionality outside of records), the following simulates apply with java methods and constructors:

(defmacro applyj
  ([mc args] `(~mc ~@args))
  ([mc x args] `(~mc ~x ~@args))
  ([mc x y args] `(~mc ~x ~y ~@args))
  ([mc x y z args] `(~mc ~x ~y ~z ~@args)))

user=> (defrecord Puffball [id name])
user.Puffball
user=> (applyj Puffball. [149 "Urist"])
#:user.Puffball{:id 149, :name "Urist"}

Upvotes: 0

Michał Marczyk
Michał Marczyk

Reputation: 84341

In Clojure 1.3 record definitions automagically introduce factory functions:

Clojure 1.3.0
user=> (defrecord Puffball [id name])
user.Puffball
user=> (apply ->Puffball [149 "Urist"])
#user.Puffball{:id 149, :name "Urist"}

->Puffball is the "positional" factory function; there's also map->Puffball which does what its name suggests.

Upvotes: 8

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