Tetramin has asked for the wisdom of the Perl Monks concerning the following question:

I am writing on a template module that allows embedding perl code which is then evaled within the modues namespace. As a side effect the templates can override a subroutines like in 

    *HSP::echo = sub {
        do something other than it normally would
    };

[download]

Running as CGI there is no problem with it. But embedding perl in HTML makes more sense when running under mod_perl. With mod_perl the modified subroutine stays modified. If someone does

    *HSP::echo = sub{ die };

then the system doesn't work anymore because it allways dies when it wants to print something out.

I know that I can make a subroutine private by saying my $sub = sub{ something private }; but since the templates are eval()ed in the same namespace it would also be possible to undef $sub. Am I lost now? Does someone know of a way how to protect a subroutine from being overridden? Something like this 

    sub echo : protected {
        do something
    }

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would be ideal maybe together with die "You are not allowed to override this subroutine".

Replies are listed 'Best First'.
Re: Overriding Subroutines in Package
by merlyn (Sage) on Oct 07, 2001 at 19:21 UTC
    If you allow Perl, you allow mischief. There's really no way around it.

    That's why packages like Template Toolkit have a "mini language" that allows most of what you need in a template without having to expose raw Perl.

    Consider that instead of writing Yet Another Templating Language, please!

    -- Randal L. Schwartz, Perl hacker

[reply]
      I know Mason and like it very much. Among the mini template tools I like the plain s/\$(\w+)/$values->{$1}/eg; most. So I combine both and it lets me write 

          <html>
    <body><h1>Hello $world</h1></body>
    </html>
    <%
      BEGIN{
       $world = "World";
      }
    %>

      [download]

      Actually no new template language, only a recombination. I wonder if I can override subroutines of Mason, too. Hopefully not.

[reply]
[d/l]
        In Template, that's 
        [% world = "World" -%]
<html> 
    <body><h1>Hello $world</h1></body> 
    </html>

        [download]
        And you don't have to expose Perl. Template is good. use Template!

        -- Randal L. Schwartz, Perl hacker

[reply]
[d/l]

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