• Laeeth Isharc (7/7) Sep 11 2015 obviously it's trivial to do with a little aa cache. and I know
• Jakob Ovrum (4/11) Sep 11 2015 Is your range random access?
• John Colvin (9/16) Sep 11 2015 perhaps
• Laeeth Isharc (3/21) Sep 11 2015 Thanks, John and Jacob.

"Laeeth Isharc" <spamnolaeeth nospamlaeeth.com> writes:

obviously it's trivial to do with a little aa cache.  and I know 
I can memoize a function, and turn the memoized version into an 
infinite range.  but suppose I have a lazy function that returns 
a finite range, and its expensive to calculate.

can I use Phobos to produce a memoized range?  So it will 
calculate on access to an element if it needs to, but will return 
the cached value if it has been calculated before.

"Jakob Ovrum" <jakobovrum gmail.com> writes:

On Friday, 11 September 2015 at 13:09:33 UTC, Laeeth Isharc wrote:
 obviously it's trivial to do with a little aa cache.  and I 
 know I can memoize a function, and turn the memoized version 
 into an infinite range.  but suppose I have a lazy function 
 that returns a finite range, and its expensive to calculate.

 can I use Phobos to produce a memoized range?  So it will 
 calculate on access to an element if it needs to, but will 
 return the cached value if it has been calculated before.

Is your range random access?

If not, `cache` should do the trick.

[1] http://dlang.org/phobos/std_algorithm_iteration.html#cache

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Friday, 11 September 2015 at 13:09:33 UTC, Laeeth Isharc wrote:
 obviously it's trivial to do with a little aa cache.  and I 
 know I can memoize a function, and turn the memoized version 
 into an infinite range.  but suppose I have a lazy function 
 that returns a finite range, and its expensive to calculate.

 can I use Phobos to produce a memoized range?  So it will 
 calculate on access to an element if it needs to, but will 
 return the cached value if it has been calculated before.

perhaps 

do what you need. An AA based cache (with a normal range 
interface if you want) is probably the sensible way to get true 
random-access here, unless you have reasonably dense and 
monotonic accesses in which case an appender-based linear cache 
could work, either using Nullable!T or a separate list of bools 
(or bits) marking whether a result is cached yet.

"Laeeth Isharc" <spamnolaeeth nospamlaeeth.com> writes:

On Friday, 11 September 2015 at 13:31:06 UTC, John Colvin wrote:
 On Friday, 11 September 2015 at 13:09:33 UTC, Laeeth Isharc 
 wrote:
 obviously it's trivial to do with a little aa cache.  and I 
 know I can memoize a function, and turn the memoized version 
 into an infinite range.  but suppose I have a lazy function 
 that returns a finite range, and its expensive to calculate.

 can I use Phobos to produce a memoized range?  So it will 
 calculate on access to an element if it needs to, but will 
 return the cached value if it has been calculated before.

 perhaps 

 would do what you need. An AA based cache (with a normal range 
 interface if you want) is probably the sensible way to get true 
 random-access here, unless you have reasonably dense and 
 monotonic accesses in which case an appender-based linear cache 
 could work, either using Nullable!T or a separate list of bools 
 (or bits) marking whether a result is cached yet.


Thanks, John and Jacob.


Laeeth.