http://tcllib.sourceforge.net/doc/tie.html
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Array persistence. This package provides a framework for the creation of persistent Tcl array variables. It is also generic enough to allow the distribution of the contents of Tcl arrays over multiple threads and processes, i.e. communication. Persistence and communication are accomplished by tying a Tcl array variable to a data source. Examples of data sources are other Tcl arrays and files.

[CMcC] 20050303 - I've written a [Metakit backend for tie]

[RLH] 20050901 - When would this be included in tcllib? With the next 8.4 release?

[AK] This can go into the example area.
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Am I using tie correctly?  The following script:

    package require tie
    set a(y) 1
    set a(z) 3
    tie::tie a file a.save
    set a(aa) 2
    set a(ab) 3
    set a(ac) 4

Gives me an error:

    can't set "a(ab)": can't unset "cache": no such variable
        while executing
    "set a(ab) 3"

[AK]: I can confirm this error. This looks very much like a bug. Please submit this (and any future) bugs to the Tcllib SourceForge project. See http://tcllib.sourceforge.net/, then follow the links to the "Bug Database" and "Submit New".

[VPT] I don't think anyone has put a bug report in for this, at least a search in the bug database didn't find "tie". I got it working by putting a catch around the "unset cache" in the  Invalidate method in the tie_file.tcl file.
This looks like a really useful module but I presume people aren't using it, at least not with files. It seems to me that if you don't use it you have to reinvent it if you want persistance of array data. 

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[Category Interprocess Communication] | [Category Package]