On 02.10.2011 18:12, Martin Nowak wrote:
I've written a wrapper to promote input ranges to buffered forward ranges.
It allows to write range agnostic lexers/parsers with infinite lookahead.
Buffering is done through a singly linked list of memory blocks that are
reference counted.
Each saved range holds a reference to all future blocks.
Blocks are recycled when being no longer used.
https://gist.github.com/1257196
Like it, but one thing catches my eye - why use GC for blocks when the
whole thing is already refcounted? Straight malloc/free would be a
better fit. Certainly it may use an allocator when we have them.
There is a major issue with the somewhat broken
implicit-save-through-copy concept.
A lot of copies in function parameters, foreach loops etc. will also create
references and thus can be easily responsible for inefficiencies.
While the concept of ForwardRange is quite elegant, I found myself
wondering on occasion that InputRange with restore could be way more
efficient. Consider:
auto r = range();
auto save_it = r; ///at least full bitwise copy and/or refCounting
if(do_stuff(r))
...
else
r = save_it;//another one
...
Compared to:
auto save_pt = r.savepoint(); //different object, minimal overhead
if(do_stuff(r))
...
else
r.restore(save_pt);//range knows how to do this efficiently
...
--
Dmitry Olshansky
