Beefy Boxes and Bandwidth Generously Provided by pair Networks
Just another Perl shrine
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

This is the only real example I could find in my own code, essentially it is a method on a base collection class to cause the collection to appear to be sorted on an arbitrary attribute (or attributes) of the objects in the collection. It uses eval to dynamically create a sort sub from a list of comparison specifications passed as an argument. Okay it doesn't fit the the 'small' criteria but I think it is illustrative of the kind of use string eval is good for:

sub sort { my ( $self, $sort_spec ) = @_; my $sort_done = 0; if ( defined $sort_spec ) { my @sort_objs; foreach my $obj ( @{$self->{_data}} ) { my $sv = []; push @{$sv}, $obj->factory_index(); foreach my $spec ( @{$sort_spec} ) { my $meth = $spec->{Key}; push @{$sv}, $obj->$meth(); } push @sort_objs, $sv; } my @comparisons = (); my $index = 0; foreach my $spec ( @{$sort_spec} ) { $index++; my $comp = ''; my ($left_arg, $right_arg) = ('$a','$b'); if ( exists $spec->{Direction} and $spec->{Direction} eq '-' ) { ( $left_arg, $right_arg) = ('$b', '$a'); } if ( $spec->{Compare} eq 'cmp' || $spec->{Compare} eq '<=>' ) { $comp = "${left_arg}->[$index] $spec->{Compare} ${right_arg} +->[$index]"; } else { $comp = "$spec->{Compare}(${left_arg}->[$index],${right_arg}- +>[$index])"; } push @comparisons, $comp; } if ( $index ) { my $sub = join ' || ' , @comparisons; $sub = "sub { $sub };"; *sortsub = eval $sub; $self->{_sort_index} = []; @{$self->{_sort_index}} = map { $_->[0] } sort sortsub @sort_objs; $sort_done = 1; my $index = 0; foreach my $obj ( $self->list() ) { $obj->factory_index($index++); } } } return $self->{_sorted} = $sort_done; }

/J\


In reply to Re: Small examples of string eval by gellyfish
in thread Small examples of string eval by spurperl

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!
  • 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, 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, 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.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others imbibing at the Monastery: (10)
    As of 2015-07-29 23:40 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (269 votes), past polls