Clojure 1.12.5

Clojure 1.12.5 has been released — a minor bugfix update for the JVM-hosted Lisp dialect that brings two targeted fixes addressing reader metadata behavior and performance optimizations in the constantly function.

What Changed in Clojure 1.12.5

The Clojure core team has shipped version 1.12.5 as a maintenance release, focusing on correctness and runtime efficiency. Two issues from the community tracker have been resolved.

• CLJ-2945 — reify reader metadata fix: A bug where reify incorrectly transferred reader metadata to the runtime object has been corrected. This ensures that metadata attached via the reader macro is no longer inadvertently passed to the created object at runtime, preventing potential data leakage and unexpected behavior in macros and code generation.
• CLJ-2228 — constantly performance improvement: The constantly function has been unrolled to remove rest args allocation. This micro-optimization reduces garbage collection pressure and improves performance in hot code paths that use constantly, such as in transducers and functional pipelines.

Why It Matters

While both fixes are narrow in scope, they address real-world issues. The reify metadata bug could cause subtle problems in libraries that rely on compile-time metadata for code generation or serialization. The constantly optimization benefits any codebase using higher-order functional patterns — a common idiom in idiomatic Clojure.

Dependency Information

Clojure 1.12.5 depends on the following core libraries and remains compatible with Java 8 bytecode, though this is expected to be the last major release series using a Java 8 baseline. Future releases will target newer Java versions.

Add the following to your project dependencies to upgrade:

[org.clojure/clojure "1.12.5"] (Leiningen) or org.clojure/clojure {:mvn/version "1.12.5"} (tools.deps).

What's Next

With version 1.12.5 shipping, the Clojure team continues to focus on stability improvements and preparing for future releases that will raise the Java baseline. Developers are encouraged to upgrade to benefit from the latest fixes.