deref.pl

use strict;
use 5.010;

{ package Class;
  sub new { my $self = bless $_[1], $_[0]; warn $self; $self }
  sub DESTROY { warn $_[0] }
}

# works
{
    my $hash = Class->new({});
    warn $hash;
}

# works
{
    my $forty_two = do { 42 };
    my $scalar = Class->new(\$forty_two);
    warn $scalar;
}

# blows up
{
    my $forty_two = \do { 42 };
    my $scalar = Class->new($forty_two);
    warn $scalar;
}
warn "end"