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Using value semantics for arrays is lovely in concept but ends up being really annoying and impractical for writing really high-performance array code. This is

Using value semantics for arrays is lovely in concept but ends up being really annoying and impractical for writing really high-performance array code. This is one of the most common complaints of library authors attempting to write fast, efficient code in Matlab and is one of the many reasons why one ends up having to write all performance-critical code in C using Matlab data structures. Clojure is reputed to get remarkable performance on a broad variety of data structures, but I've had a hard time finding benchmarks comparing Clojure's purely functional arrays with normal linearly indexed arrays – if you have some references to such comparisons, I'd love to see them. In my experience, nothing beats a plain old linearly indexed, mutable array when that's what you need. Making that basic structure unavailable in a language intended for high-performance numerical computing strikes me as utterly perverse.

cgag 13y ago
Clojure gets great performance with its immutable data structures, but no one pretends they're as fast as plain native java arrays or using mutation. It's normal in the Clojure community to drop down to using arrays or transients (http://clojure.org/transients http://clojure.org/transients) in high performance functions and then convert the result back to an immutable data structure. As long as you still present a pure interface, no one knows or cares what kind of mutation you do internally.
ScottBurson 13y ago
Oh, I wouldn't suggest making plain old mutable arrays unavailable. I totally agree that library authors and sophisticated users need access to them (and preferably not by dropping into C). I just think the array and other collection types presented to users for ordinary application-level programming should be functional. Mutable types should stay in an "advanced topics" section of the manual.
- marcosdumay 13y ago
  That's a bad an completely not intuitive trade-off for a language that is expected to be fast. I've first studied Julia today, but just by knowing its niche I already expected it to use reference semantics, not value. It'd be quite confusing if the examples demonstrated otherwise.
  - cgag 13y ago
    As long as it's not exceedingly difficult to drop down to using mutation, having immutability by default is ridiculously nice. I don't think I appreciated it fully until I used Clojure a significant amount, but using languages with reference semantics feels disgusting now.
gfodor 13y ago
Iirc clojure lets you get your hands on a mutable array for performance via the transient keyword. The contract is such that you can do what you want (fast things) in the transient block, but it's a black box to outside callers who never see the array in its mutable form. Ie the function is still a pure function since no side effects leak. http://clojure.org/transients http://clojure.org/transients
- moomin 13y ago
  I'm going to nitpick horribly here: in Clojure, an array is just a Java array. But what most people use are vectors, which are immutable. 'transient' returns a mutable vector, not an array.

cgag 13y ago

Clojure gets great performance with its immutable data structures, but no one pretends they're as fast as plain native java arrays or using mutation. It's normal in the Clojure community to drop down to using arrays or transients (http://clojure.org/transients http://clojure.org/transients) in high performance functions and then convert the result back to an immutable data structure. As long as you still present a pure interface, no one knows or cares what kind of mutation you do internally.

ScottBurson 13y ago

Oh, I wouldn't suggest making plain old mutable arrays unavailable. I totally agree that library authors and sophisticated users need access to them (and preferably not by dropping into C). I just think the array and other collection types presented to users for ordinary application-level programming should be functional. Mutable types should stay in an "advanced topics" section of the manual.

marcosdumay 13y ago
That's a bad an completely not intuitive trade-off for a language that is expected to be fast. I've first studied Julia today, but just by knowing its niche I already expected it to use reference semantics, not value. It'd be quite confusing if the examples demonstrated otherwise.
- cgag 13y ago
  As long as it's not exceedingly difficult to drop down to using mutation, having immutability by default is ridiculously nice. I don't think I appreciated it fully until I used Clojure a significant amount, but using languages with reference semantics feels disgusting now.

gfodor 13y ago

Iirc clojure lets you get your hands on a mutable array for performance via the transient keyword. The contract is such that you can do what you want (fast things) in the transient block, but it's a black box to outside callers who never see the array in its mutable form. Ie the function is still a pure function since no side effects leak. http://clojure.org/transients http://clojure.org/transients

moomin 13y ago
I'm going to nitpick horribly here: in Clojure, an array is just a Java array. But what most people use are vectors, which are immutable. 'transient' returns a mutable vector, not an array.