DBI internals actually allocate the array that is returned by fetch_xxxref() - DBD::Sybase just fills each item as needed.

DBI also sets this array "read-only", which I had to work-around as Sybase can return multiple result sets with varying number of columns.

So DBD::Sybase has this code in the fetch routine: 

    av = DBIS->get_fbav(imp_sth);
    num_fields = AvFILL(av)+1;

    /* XXX
       The code in the if() below is likely to break with new versions
       of DBI!!! */
    if(num_fields < imp_sth->numCols) {
    int isReadonly = SvREADONLY(av);
    if(isReadonly)
        SvREADONLY_off(av);        /* DBI sets this readonly  */
    i = imp_sth->numCols - 1;
    while(i >= num_fields)
        av_store(av, i--, newSV(0));
    num_fields = AvFILL(av)+1;
    if(isReadonly)
        SvREADONLY_on(av);        /* protect against shift @$row etc *
+/

[download]
To summarize - the array that is referenced by $data in the code snippet above is read-only, but each of the items in the array are read-write (hence the assignment to @$data fails, but setting $_ for each undef item works).

Michael

In reply to Re: Re: Modification of a read-only by mpeppler
in thread Modification of a read-only by Jonathan

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.