Does Clojure have an equivalent of Java's try-with-resources construct?
If not, what is the normal way to handle this idiom in Clojure code?
The pre-Java-7 idiom for safely opening and closing resources is verbose enough that they actually added support for try-with-resources to the language. It seems strange to me that I can't find a macro for this use case in the standard Clojure library.
An example to a mainstream Clojure-based project repository—showing how this issue is handled in practice—would be very helpful.
You can use with-open to bind a resource to a symbol and make sure the resource is closed once the control flow left the block.
The following example is from clojuredocs:
(with-open [r (clojure.java.io/input-stream "myfile.txt")]
(loop [c (.read r)]
(when (not= c -1)
(print (char c))
(recur (.read r)))))
It will be expanded to the following:
(let [r (clojure.java.io/input-stream "myfile.txt")]
(try
(loop [c (.read r)]
(when (not= c -1)
(print (char c))
(recur (.read r))))
(finally (.close r))))
As you can see, a let
block is created with a try
and finally
to the call .close()
method.