These new functions are intended only for development-time interactive use at the repl - using a deps.edn is still the proper way to build and maintain production code. To this end, these functions all check that *repl* is bound to true (that flag is bound automatically by clojure.main/repl). In a clojure.main REPL, these new functions are automatically referred in the user namespace. In other repls, you may need to (require '[clojure.repl.deps :refer :all]) before use.

Library resolution and download are provided by tools.deps. However, you do not want to add tools.deps and its many dependencies to your project classpath during development, and thus we have also added a new api for invoking functions out of process via the Clojure CLI.

There are many useful tools you can use at development time, but which are not part of your project’s actual dependencies. The Clojure CLI provides explicit support for tools with their own classpath, but there was not previously a way to invoke these interactively.

Clojure now includes clojure.tools.deps.interop/invoke-tool to invoke a tool function out of process. The classpath for the tool is defined in deps.edn and you do not need to add the tool’s dependencies to your project classpath.

add-lib functionality is built using invoke-tool but you can also use it to build or invoke your own tools for interactive use. Find more about the function execution protocol on the CLI reference.

Programmers can now use qualified methods as ordinary functions in value contexts - the compiler will automatically generate the wrapping function. The compiler will generate a reflective call when a qualified method does not resolve due to overloading. Developers can supply :param-tags metadata on qualified methods to specify the signature of a single desired method, 'resolving' it.

Qualified method invocations with :param-tags use only the tags to resolve the method. Without param-tags they behave like the equivalent dot syntax, except the qualifying class takes precedence over hints of the target object, and over its runtime type when invoked via reflection.

Note: Static fields are values and should be referenced without parens unless they are intended as function calls, e.g (System/out) should be System/out. Future Clojure releases will treat the field’s value as something invokable and invoke it.

Developers can supply :param-tags metadata on qualified methods to specify the signature of a single desired method, 'resolving' it. The :param-tags metadata is a vector of zero or more tags: [tag …​]. A tag is any existing valid :tag metadata value. Each tag corresponds to a parameter in the desired signature (arity should match the number of tags). Parameters with non-overloaded types can use the placeholder _ in lieu of the tag. When you supply :param-tags metadata on a qualified method, the metadata must allow the compiler to resolve it to a single method at compile time.

A new metadata reader syntax ^[tag …​] attaches :param-tags metadata to member symbols, just as ^tag attaches :tag metadata to a symbol.

Developers can now refer to an array class using a symbol of the form ComponentClass/#dimensions, eg String/2 refers to the class of a 2 dimensional array of Strings. Component classes can be fully-qualified classes, imported classes, or primitives. Array class syntax can be used as both type hints and values.

Examples: String/1, java.lang.String/1, long/2.

Java APIs increasingly return Streams and are hard to consume because they do not implement interfaces that Clojure already supports, and hard to interop with because Clojure doesn’t directly implement Java functional interfaces.

In addition to functional interface support, Clojure now provides these functions to interoperate with streams in an idiomatic manner, all functions behave analogously to their Clojure counterparts:

All of these operations are terminal stream operations (they consume the stream).

Partitioning of a collection uses a series of takes (to build a partition) and drops (to skip past that partition). CLJ-2713 adds a new internal interface (IDrop) indicating that a collection can drop more efficiently than sequential traversal, and implements that for persistent collections and algorithmic collections like range and repeat. These optimizations are used in drop, nthrest, and nthnext.

Additionally, there are new functions partitionv, partitionv-all, and splitv-at that are more efficient than their existing counterparts and produce vector partitions instead of realized seq partitions.

Interning a var in a namespace (vs aliasing) must create a stable reference that is never displaced, so that all references to an interned var get the same object. There were some cases where interned vars could get displaced and those have been tightened up in 1.12.0-alpha1. If you encounter this situation, you’ll see a warning like "REJECTED: attempt to replace interned var #'some-ns/foo with #'other-ns/foo in some-ns, you must ns-unmap first".

This addresses the root cause of an issue encountered with Clojure 1.11.0, which added new functions to clojure.core (particularly abs). Compiled code from an earlier version of Clojure with var names that matched the newly added functions in clojure.core would be unbound when loaded in a 1.11.0 runtime. In addition to CLJ-2711, we rolled back a previous fix in this area (CLJ-1604).