Numerics, boxing, and primitives

Numerics are scalars. The discussion on numerics was deferred till this chapter for the sole reason that the numerics implementation in Clojure has strong Java underpinnings. Since version 1.3, Clojure has settled with 64-bit numerics as the default. Now, long and double are idiomatic and the default numeric types. Note that these are primitive Java types, not objects. Primitives in Java lead to high performance and have several optimizations associated with them at compiler and runtime levels. A local primitive is created on the stack (hence does not contribute to heap allocation and GC) and can be accessed directly without any kind of dereferencing. In Java, there also exist object equivalents of the numeric primitives, known as boxed numerics—these are regular objects that are allocated on the heap. The boxed numerics are also immutable objects, which mean not only does the JVM need to dereference the stored value when reading it, but also needs to create...