I see. Thanks, that makes a lot of sense. So just because this sort of multiple reference isn't explicit (or even visible) in Clojure, that doesn't mean it's not happening. Under the hood, a derived data structure is more than likely to share memory with its progenitor. And that's for very good performance reasons (option b in my C++ comparison).
But doesn't that all that data-sharing happen in tree-like structures under the careful control of the compiler? I find myself wondering whether circular references need remain a possibility in this context. Perhaps we could still consider a simple reference-counting mechanism (much like the one you mention, boost::shared_ptr<>). Thanks Alistair On Dec 25, 5:38 pm, mac <markus.gustavs...@gmail.com> wrote: > On Dec 24, 6:14 pm, atucker <agjf.tuc...@googlemail.com> wrote: > > > > > I am also curious about this. Apologies, possibly naive question > > ahead :) > > > My background is in C++. By choosing to work with immutable values > > (i.e. with a lot of consts), I found that I was able to avoid most of > > explicit memory management, pointers etc. Exceptions were: > > > (a) when interfacing with other people's code, and > > (b) when making optimisations, e.g. to save a needless copy-on-return. > > > Otherwise everything happened behind the scenes as variables with > > "automatic" lifespan, passing into and out of scope, had their memory > > allocated and deallocated on the stack. > > > Surely this is the most performant approach to memory management where > > it is possible? And doesn't Clojure's pure-functional ethos make it > > possible? > > > Alistair > > It's great until you want to have more than one reference to a > particular piece of data. > Then you have two options: > a) Copy > b) Make another pointer to it > > Option a) is often good enough. But if it's a huge object (like sound > or picture data) you probably can't afford copying it. > > Option b) means that you now have lost the ability to manage the > memory through scope alone. You will need manual management or some > kind of GC mechanism. In C++ you often use boost::shared_ptr<> but > that can't handle circular references so there is still a manual > management component to it. > > When option a) is too expensive and option b) is too complicated, > that's when you need a real GC. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
