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From: Lukasz Stafiniak <lukstafi@gmail.com>
Date: Wed, 14 Mar 2012 22:12:29 +0100
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To: Edgar Friendly <thelema314@gmail.com>
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Subject: Re: [Caml-list] Tuples (covariant immutable arrays)

On Wed, Mar 14, 2012 at 10:03 PM, Edgar Friendly <thelema314@gmail.com> wrote:
> Batteries has a Cap submodule that provides type-level protection for arrays
> so they can be Read-only/Write-only/Read-write.  The same idea with a
> variance annotation and just read-only access seems to be what you're
> looking for, no?

It seems no, because Cap is invariant, and for a reason: for example,
Hashtbl.Cap.of_table says
"This operation involves no copying. In other words, in let cap =
of_table a in ..., any modification in a will also have effect on cap
and reciprocally."

What I'm thinking about is  type +'a Tuple.t with Tuple.of_list and
Tuple.of_array both performing a copy.