Re: [Caml-list] two unrelated questions

[John Max Skaller <skaller@ozemail.com.au>]

Brian Rogoff wrote:

> > It's a pity there is no such destructor for a Hashtbl.
> > [All C++ STL data structures have read iterators, which
> > amount to destructors]
> 
> Are they really the same? I think of STL style iterators as being more
> similar to array indices, and arrays (and hashtables) are not defined
> inductively like lists, trees, and graphs, etc.

	Well, for an iterator p, there are three operations:

	*p
	p++
	p==q

But they're usually combined like:

	*p++

which is equivalent to getting one element of the container p denotes,
and adjusting p to denote the rest of the container.

> As I'm sure you know, there is an easy enough transformation from
> hashtables (and arrays) to lists, like the following
> 
> let pairs_of_hashtbl ht =
>   let pl_ref = ref [] in
>   let fn a b = (pl_ref := (a,b)::(!pl_ref) in
>   (Hashtbl.iter fn ht; !pl_ref)

	Sure, but this requires building a new data structure.
Even if that is OK for traversal, it can't handle mutating
operations.

	Of course, people don't use STL algorithms as much in C++
as they might, because there is no support for nested anonymous
functions (lambdas) or currying, which are essential for localisation.
And of course Ocaml is _good_ at that :-)

-- 
John (Max) Skaller, mailto:skaller@maxtal.com.au
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