如何将运算符传递给Perl子例程？

Question

我有一个名为"lookup"的子程序,它在给定值的哈希中执行查找.我意识到如果我可以要求它看不到给定的值,而是小于作为参数传递的值,那将会更强大.

我可以使lookupbigger,lookupsmall等等,但我相信有更好的方法.

# lookup id according to the search criteria
sub lookup {
  my( $data, $lk, $lv ) = ( @_ );
  my @res;

  foreach my $key (keys $data) {
    my $value = $$data{$key};
    next unless( defined $$value{$lk} );
    # this is the line where I want to replace eq with another operator
    push(@res, $key) if( $$value{$lk} eq $lv );
  }

  return \@res;
}

Answer 1

您可以将标准函数传递给查找函数:

#!/usr/bin/env perl

use strict; use warnings;
use YAML;

my %hash = qw(a 1 b 2 c 3 d 4 e 5);

# find all keys with odd values

print Dump lookup_keys_by_value(\%hash, sub {
        return unless @_;
        my $v = shift;
        return $v % 2;
    },
);

sub lookup_keys_by_value {
    my ($hash, $criterion) = @_;

    my @keys;

    while (my ($k, $v) = each %$hash) {
        push @keys, $k if $criterion->($v);
    }

    return \@keys;
}