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Using scalar as conditions in perl

First timer ... so let me know if there is something that I did not pay attention to when asking a question.

The question is how to use the scalar as a condition, since the code below does not work.

my @parameter=('hub');

my %condition;
$condition{'hub'}{'1'}='$degree>=5';

foreach (@parameter) {
       if ($condition{$_}{'1'}) {..}
}

I thought this was because the condition was not interpreted correctly, so I also tried the following, which also did not work.

if ("$condition{$parameter}{'1'}") { ..}

It would be very helpful to help. :)

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3 answers

You either need an eval string that evaluates the string as perl code

if (eval $condition{$_}{'1'}) { ...

or perhaps a safer approach would be to use code links

$condition{'hub'}{'1'} = sub { return $degree>=5 };

if ($condition{$_}{'1'}->()) { ...

. $var->() .

+11

, , - '$ degree >= 5' . , ( eval), , . , :

sub generate_condition {
    my ( $test, $bound ) = @_;
    return sub { return $test >= $bound; };
}

my %condition;
$condition{'hub'}{'1'} = generate_condition( $degree, 5 );

if( $condition{$parameter}{1}->() ) { ... }

, , >= (.. ) . . eval ( ). generate_condition() sub.

generate_condition() , , .

, Perl , . subref :

use strict;
use warnings;
use feature qw/state/;

sub generate_condition {
    my ( $test, $relation, $bound ) = @_;
    die "Bad relationship\n" 
        if ! $relation =~ m/^(?:<=?|>=?|==|l[te]|g[te]|cmp)$/;
    state $relationships = {
        '<'     => sub { return $test <   $bound },
        '<='    => sub { return $test <=  $bound },
        '=='    => sub { return $test ==  $bound },
        '>='    => sub { return $test >=  $bound },
        '>'     => sub { return $test >   $bound },
        '<=>'   => sub { return $test <=> $bound },
        'lt'    => sub { return $test lt  $bound },
        'le'    => sub { return $test le  $bound },
        'eq'    => sub { return $test eq  $bound },
        'ge'    => sub { return $test ge  $bound },
        'gt'    => sub { return $test gt  $bound },
        'cmp'   => sub { return $test cmp $bound },
    };
    return $relationships->{$relation};
}


my $true_condition  = generate_condition( 10, '>', 5 );
my $false_condition = generate_condition( 'flower', 'eq', 'stamp' );

print '10 is greater than 5: ', 
      $true_condition->()  ? "true\n" : "false\n";
print '"flower" is equal to "stamp": ', 
      $false_condition->() ? "true\n" : "false\n";

, , , , . , "$bound" "$ ratio", "$test" . :

sub generate_condition {
    my ( $relation, $bound ) = @_;
    die "Bad relationship\n" 
        if ! $relation =~ m/^(?:<=?|>=?|==|l[te]|g[te]|cmp)$/;
    state $relationships = {
        '<'     => sub { return $_[0]  <   $bound },
        # ......

:

my $condition = generate_condition( '<', 5 );
if( $condition->(2) ) {
    print "Yes, 2 is less than 5\n";
}

, , :

sub generate_condition {
    my $relation = shift;
    die "Bad relationship\n" 
        if ! $relation =~ m/^(?:<=?|>=?|==|l[te]|g[te]|cmp)$/;
    state $relationships = {
        '<'     => sub { return $_[0]  <   $_[1] },
        '<='    => sub { return $_[0]  <=  $_[1] },
        # ...... and so on .....
    return $relationship->($relation);
}

my $condition = generate_condition( '<' );
if( $condition->(2,10) ) { print "True.\n"; }

Perl

+4

? true, .

themel@kallisti: ~ $ perl -e 'print "oops\n" if "false" ; '
oops
themel@kallisti: ~ $ perl -e 'print "oops\n" if "" ; '
themel@kallisti: ~ $ perl -e 'print "oops\n" if "\$degree < 5" ;'
oops

, eval. :

my @conds=('$foo>42', '$foo>23');
my $foo = 33;

foreach my $cond(@conds) { 
    print "$cond itself was true\n" if $cond;
    print "$cond evaluated to true\n" if eval($cond);
}


$foo>42 itself was true
$foo>23 itself was true
$foo>23 evaluated to true
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