The check would be done only once

#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
use Syntax::Construct qw{ // };


{   package Array::Nonempty;

    use Tie::Array;
    use parent -norequire => 'Tie::StdArray';
    use Carp;

    sub CLEAR {
        my $self = shift;
        $self->[0] = [];
    }

    sub TIEARRAY {
        my ($class, $untie) = @_;
        bless [ [], $untie ], $class
    }

    sub EXTEND {
        my ($self, $size) = @_;
        croak "Cannot be empty" if 0 == @{ $self->[0] } && 0 == $size;
        $self->SUPER::EXTEND($size);

        # Prevent "untie attempted while 1 inner references still exis
+t"
        my $untie = $self->[1];
        undef $self;

        untie @$untie;
    }

}


{   package UNIVERSAL;
    use Attribute::Handlers autotieref => { Nonempty => 'Array::Nonemp
+ty' };
}

my @list = 1 .. 5;

for (1 .. 10) {
    my @check :Nonempty = @list;
    shift @list;
    say tied(@check) // 'not tied';
    say "@check";
}
[download]

Wrong I was, young padawan. ;-)

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Interesting...

I had the model for CODE attributes in mind which happen at compile time:

(excerpt from attributes )

3.

    Code:

            package X;
            sub foo : lvalue ;

    Effect:

            use attributes X => \&foo, "lvalue";
[download]

That's why Attribute::Handlers is putting such emphasis onto the compilation phase when the association happens.

but LEXICAL attributes seem to call import with each declaration at run-time (which is consistent with the fact that my has a compile and a run-time effect.)

2.

    Code:

            package Felis;
            my $cat : Nervous;

    Effect:

            use attributes ();
            attributes::->import(Felis => \$cat, "Nervous");
[download]

maybe Attribute::Handlers should be clearer about this?

> There are ways how not to be wrong.

(A disturbance in the Force happens)

Now more potential in using attributes I see ... ;-) ¹

Cheers Rolf
_{(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!}

update

¹) to be more specific ... this behaviour means that the untie happens almost immediately after the tie, i.e. the potential for possible ugly side effects is practically zero.

this behaviour means that the untie happens almost immediately after the tie, i.e. the potential for possible ugly side effects is practically zero.

My benchmarks show attributes are much slower than a (&;@) sub, especially for short lists (many thousand times).

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]