COMMENT(!MOD!zsh/db/gdbm
Builtins for managing associative array parameters tied to GDBM databases.
!MOD!)
The tt(zsh/db/gdbm) module is used to create "tied" associative arrays
that interface to database files.  If the GDBM interface is not available,
the builtins defined by this module will report an error.  This module is
also intended as a prototype for creating additional database interfaces,
so the tt(ztie) builtin may move to a more generic module in the future.

The builtins in this module are:

startitem()
findex(ztie)
cindex(database tied array, creating)
item(tt(ztie -d db/gdbm -f) var(filename) [ tt(-r) ] var(arrayname))(
Open the GDBM database identified by var(filename) and, if successful,
create the associative array var(arrayname) linked to the file.  To create
a local tied array, the parameter must first be declared, so commands
similar to the following would be executed inside a function scope:

example(local -A sampledb
ztie -d db/gdbm -f sample.gdbm sampledb)

The tt(-r) option opens the database file for reading only, creating a
parameter with the readonly attribute.  Without this option, using
`tt(ztie)' on a file for which the user does not have write permission is
an error.  If writable, the database is opened synchronously so fields
changed in var(arrayname) are immediately written to var(filename).

Changes to the file modes var(filename) after it has been opened do not
alter the state of var(arrayname), but `tt(typeset -r) var(arrayname)'
works as expected.
)
findex(zuntie)
cindex(database tied array, destroying)
item(tt(zuntie) [ tt(-u) ] var(arrayname) ...)(
Close the GDBM database associated with each var(arrayname) and then
unset the parameter.  The tt(-u) option forces an unset of parameters
made readonly with `tt(ztie -r)'.

This happens automatically if the parameter is explicitly unset or its
local scope (function) ends.  Note that a readonly parameter may not be
explicitly unset, so the only way to unset a global parameter created with
`tt(ztie -r)' is to use `tt(zuntie -u)'.
)
enditem()

The fields of an associative array tied to GDBM are neither cached nor
otherwise stored in memory, they are read from or written to the database
on each reference.  Thus, for example, the values in a readonly array may
be changed by a second writer of the same database file.
