You could speed up the latter by using the hook formulation, which is supported 
by special code.  To wit:

reshape=:$ ,
memcopy=:$ reshape ]

That said, I haven't checked whether this has copy-by-reference or -value 
semantics for mmapped nouns.

-Dan


Please excuse typos; composed on a handheld device.

-----Original Message-----
From: Ian Clark <[email protected]>
Sender: [email protected]
Date: Sat, 28 May 2011 22:38:00 
To: Programming forum<[email protected]>
Reply-To: Programming forum <[email protected]>
Subject: Re: [Jprogramming] decoupling assignments to mapped files

Thanks, Dan.

Works nicely, and is slightly faster than: $ $ ,

Ian


On Sat, May 28, 2011 at 12:52 AM, Dan Bron <[email protected]> wrote:
> Ian asked:
>>  Can you think of a low-overhead verb which
>>  will force J to allocate sav its own separate
>>  space in memory?
>
> Try a:&{
>
>           load'jmf'
>           createjmf_jmf_ 400;~fn=.jpath'~temp\F.jmf'
>           map_jmf_ 'F';fn
>
>           F=:'hello there'
>
>           G=:a:{F
>           G=:'goodbye here'
>
>           F
>        hello there
>
> Roger will make no guarantees about this behavior or any way to force a
> memcopy.
>
> -Dan
>
>
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