Been experimenting with mapped files...
Looking for a reliable way to detect if a mapped file has changed
since I last inspected it.
If pronoun: TITLE is mapped to a file, then
sav=: TITLE
will create: sav -as not a copy but an alias of TITLE. (Not
surprisingly, because they share the same memory.)
Thus reassigning sav will change TITLE too, and vice-versa. Which
makes: sav=:TITLE no good as a way of snapshotting TITLE to detect
changes.
1. Can you think of a low-overhead verb: own -used like so:
sav=: own TITLE
-which will force J to allocate sav its own separate space in memory?
I've tried these:
own=: ]
own=: [: > [: {: 0 ; <
own=: $ $ ]
The first 2 don't work: sav keeps in step with TITLE, thanks to J's
optimisation.
The third defn works --but for how much longer? At some future date it
might break, thanks to improved J optimisation.
2. Is there a more elegant way of checking whether a mapped file has changed?
When I change a mapped noun I cannot see any changes to:
showmap_jmf_'' --this is on a Mac.
I can repeatedly read the directory entry using 1!:0 and watch for
it to change (as its timestamp gets updated). The processing overhead
is tolerable, but is it the best I can do?
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