new std.variant (was Re: The Right Approach to Exceptions)

Jonathan M Davis jmdavisProg at
Wed Feb 22 12:17:09 PST 2012

On Wednesday, February 22, 2012 14:12:07 Jonathan M Davis wrote:
> On Wednesday, February 22, 2012 12:16:43 Robert Jacques wrote:
> > There's a big difference between sealed and not accessible. .data's API
> > requires exposing an array, and there's no way to do this without leaking
> > memory like a sieve in one way or another. However, if all you need is to
> > iterate the contents, that's easy to do. I'm currently adding backwards
> > iteration. Even indexing is fairly efficient (not yet implemented),
> > particularly relative indexing (i.e. n from back or front).
> > 
> > I haven't seen too many use cases yet where accessing the underlying array
> > is important, nor has it come up on bugzilla. I've found one case in
> > Phobos where appender was used as a stack. What's your example? What
> > features does it have to support and how efficient does it have to be?
> It's can be useful to just get at the underlying array and pass it to
> functions which are going to use it but not alter it (or at least not append
> to it). Iterating over it doesn't give you an array. And since appender's
> entire purpose is simply to make appending to an array more efficient,
> making it impossible to treat it as one until you're done appending is
> overly restrictive IMHO. Yes, if you leak references to the underlying
> data, you're asking for trouble, but that doesn't mean that it can't be
> used without leaking memory.
> Unfortunately, I don't have any code snippets with me at the moment, so I
> can't give any concrete examples of usage, but any situation where you want
> to be able to operate on the array while building it needs the ability to
> get at the underlying array. Yes, in most cases, you're probably simply
> appending to the array, but at least once in a while, you need to operate
> on an array while building it.

Also, wouldn't it be less efficient if you _had_ to copy the array once you were 
done with the appender? That would seem to go against what appender is trying 
to do.

- Jonathan M Davis

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