[phobos] enforce() in std.container.Array

[Jonathan M Davis]

On Friday, November 19, 2010 05:55:52 David Simcha wrote:
> I'm looking to try out std.container.Array for a few huge arrays that
> the GC isn't cutting it for.  I noticed that this container is always
> bounds checked via enforce().  This has huge performance costs:
> 
> import std.stdio, std.container, std.datetime;
> 
> void main() {
>      Array!uint arr;
>      arr.length = 10_000_000;
>      //auto arr = new uint[10_000_000];
>      auto sw = StopWatch(autoStart);
>      foreach(i; 0..arr.length) {
>          arr[i] = i;
>      }
> 
>      writeln(sw.peek.milliseconds);
> }
> 
> This benchmark takes about 86 milliseconds with -O -inline -release.
> When I use the builtin version instead (comment out the
> std.container.Array stuff and uncomment the uint[] stuff) it only takes
> about 18 milliseconds.  Should I change front(), popFront(), opIndex(),
> etc. to be templates that use assert and give the caller's line and file
> on failure, just like regular builtin arrays?

Well, as long as the assertions have error messages which make it very clear 
that it's the user of Array that's screwing up and not the developers or Array, 
it seems to me to be a very good idea. One thing that would be interesting to 
look at though would be the cost if enforce weren't lazy. That wouldn't account 
for the whole cost (maybe even very little of it), but it would be interesting 
to look at - especially if the enforce calls in question don't need the laziness 
for their message arguments.

- Jonathan M Davis.