> Immutable data structures are always going to be slower than their mutable cousins.
True in general, but only if you just care about single core performance. A data structure that allows your algorithm to scale gracefully to more cores is actually more performant than a data structure that's faster for a single thread, but is extremely hard to scale in concurrent settings. Clojure sacrifices single-thread performance for multithreaded scaling, and it's the right tradeoff given current hardware trends (for example, consider the design of Clojure's reducers, and how it focuses on multi-core scaling).
My main concern with immutable data structures (and most data structures designed to work in concurrent settings, actually), is their heavy reliance on garbage collection, and on old-gen garbage collection in particular. Old-gen GC still has some ways to go, at least in HotSpot.
True in general, but only if you just care about single core performance. A data structure that allows your algorithm to scale gracefully to more cores is actually more performant than a data structure that's faster for a single thread, but is extremely hard to scale in concurrent settings. Clojure sacrifices single-thread performance for multithreaded scaling, and it's the right tradeoff given current hardware trends (for example, consider the design of Clojure's reducers, and how it focuses on multi-core scaling).
My main concern with immutable data structures (and most data structures designed to work in concurrent settings, actually), is their heavy reliance on garbage collection, and on old-gen garbage collection in particular. Old-gen GC still has some ways to go, at least in HotSpot.