perl - 使用来自另一个包的排序子程序

Question

我有一个脚本和一个包，如下所示:

# file: sortscript.pl
use strict;
use warnings;
use SortPackage;

my @arrays = ([1,"array1"],[10,"array3"],[4,"array2"]);

print "Using sort outside package\n";
foreach (sort SortPackage::simplesort @arrays){
    print $_->[1],"\n";
}

print "\nUsing sort in same package\n";
SortPackage::sort_from_same_package(@arrays);

——

# file: SortPackage.pm
use strict;
use warnings;
package SortPackage;

sub simplesort{
    return ($a->[0] <=> $b->[0]);
}

sub sort_from_same_package{
    my @arrs = @_;
    foreach (sort simplesort @arrs){
        print $_->[1],"\n";
    } 
}
1;

运行脚本产生输出:

$ perl sortscript.pl
Using sort outside package
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
Use of uninitialized value in numeric comparison (<=>) at SortPackage.pm line 15.
array1
array3
array2

Using sort in same package
array1
array2
array3

当子程序在另一个包中时，为什么我不能正确使用它进行排序？

Answer 1

如前所述，$a和 $b是包全局变量，因此另一种解决方案是将调用站点的全局变量临时别名为包 SortPackage 中的全局变量。 :

{
    local (*a, *b) = (*SortPackage::a, *SortPackage::b);
    foreach (sort SortPackage::simplesort @arrays){
        print $_->[1],"\n";
    }
}

但这当然很丑陋。我只要 SortPackage导出一个完整的排序例程，而不仅仅是一个比较器:

package SortPackage;
use strict;

sub _sort_by_first_element_comparator {
    return $a->[0] <=> $b->[0];
}

sub sort_by_first_element {
    return sort _sort_by_first_element_comparator @_;
}