When using closures you often see a syntax something like this:

my $function_ref = my_closure($stuff);
for ( my $data = $function_ref->() ) {
#   do things
}

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However when working on some code to sort DNS resource records (previously stored in a HoA), the syntax below works and using $sortby->() doesn't:

for ( qw{ NS MX TXT HINFO SPF SRV A CNAME PTR } ) {
    if ( exists $dns_records{$_} ) {
        print_header("$_");
        my $sortby = setsort($_);
        for my $rec ( sort $sortby @{$dns_records{$_}} ) {
            print $rec, "\n";
        }
    }
}

sub setsort {
    my $type = shift;
    return sub { $a <=> $b } if ( uc($type) eq "PTR" );
    return sub { $a cmp $b };
}

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The error I get when using $sortby->() is as follows (line number changed to correspond to the above sample):

Array found where operator expected at ./sample.pl line 5, at end of l
+ine
        (Missing operator before ?)

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Partial answer while writing this question -- sort's BLOCK is an anonymous code reference, and $sortby is also an anonymous code reference. $sortby->() is a dereferenced function reference, which isn't what sort wants at all.

However, any insight into the error message that results is appreciated!

David.

In reply to Syntax question about closures and Perl 'sort' by dwm042

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