获取 function 返回的列表的第一项

Question

A simple simulation of the problem:

use strict;
use warnings;

sub uniq
{
  my %seen;
  grep !$seen{$_}++, @_;
}

my @a = (1, 2, 3, 1, 2);

print shift @{uniq(@a)}; 

Can't use string ("3") as an ARRAY ref while "strict refs" in use

Answer 1

Need to impose a list context on the function call, and then pick the first element from the list.

The print , or any other subroutine call, already supplies a list context. Then one way to extract an element from a returned list

print +( func(@ary) )[0];

This disregards the rest of the list.

That + is necessary (try without it), unless we equip print itself with parentheses around all its arguments, that is

print( (func(@ary))[0] );

Answer 2

One option could be to return an array reference:

sub uniq {
  my %seen;
  [grep !$seen{$_}++, @_];
}

Answer 3

If uniq returned an array reference, then @{uniq(...)} would be the correct idiom to get an array (which is a suitable argument for shift ). For a more general list, you can cast the list to an array reference and then dereference it.

print shift @{ [ uniq(@a) ] };