There is hardly any difference between

    my @foo;
    my %bar;
[download]

and

    my @foo = ();
    my %bar = ();
[download]

Both will declare the variables at compile time, and assign an empty list to them at run time. Using Devel::Peek shows there is no difference.

#!/usr/bin/perl

use strict;
use warnings 'all';
use Devel::Peek;

my @foo_1;
my @foo_2 = ();
my %bar_1;
my %bar_2 = ();

print STDERR "\@foo_1:\n";
Dump (\@foo_1);
print STDERR "\@foo_2:\n";
Dump (\@foo_2);
print STDERR "\%bar_1:\n";
Dump (\%bar_1);
print STDERR "\%bar_2:\n";
Dump (\%bar_2);
__END__
[download]

@foo_1:
SV = RV(0x81584b4) at 0x814490c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x814ead4
  SV = PVAV(0x8145e5c) at 0x814ead4
    REFCNT = 2
    FLAGS = (PADBUSY,PADMY)
    IV = 0
    NV = 0
    ARRAY = 0x0
    FILL = -1
    MAX = -1
    ARYLEN = 0x0
    FLAGS = (REAL)
@foo_2:   
SV = RV(0x81584b4) at 0x814490c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x814eaec
  SV = PVAV(0x8145e28) at 0x814eaec
    REFCNT = 2 
    FLAGS = (PADBUSY,PADMY)
    IV = 0
    NV = 0
    ARRAY = 0x0
    FILL = -1
    MAX = -1   
    ARYLEN = 0x0
    FLAGS = (REAL)
%bar_1:
SV = RV(0x81584b4) at 0x814490c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x814eb10
  SV = PVHV(0x81535b8) at 0x814eb10
    REFCNT = 2  
    FLAGS = (PADBUSY,PADMY,SHAREKEYS)
    IV = 0
    NV = 0
    ARRAY = 0x0
    KEYS = 0
    FILL = 0   
    MAX = 7  
    RITER = -1
    EITER = 0x0 
%bar_2:
SV = RV(0x81584b4) at 0x814490c
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x814eba0
  SV = PVHV(0x81535f0) at 0x814eba0
    REFCNT = 2
    FLAGS = (PADBUSY,PADMY,SHAREKEYS)
    IV = 0
    NV = 0
    ARRAY = 0x0
    KEYS = 0   
    FILL = 0 
    MAX = 7    
    RITER = -1  
    EITER = 0x0   

However, there is a big difference between

my $yuk;
[download]

and

my $yuk = {};
[download]

The former assigns an undefined value to $yuk, while the latter assigns a reference to an anonymous hash to $yuk.

Devel::Peek will show the difference:

#!/usr/bin/perl

use strict; 
use warnings 'all'; 
use Devel::Peek;
  
my $yuk_1;
my $yuk_2 = {};
    
print STDERR "\$yuk_1:\n";
Dump ($yuk_1); 
print STDERR "\$yuk_2:\n";
Dump ($yuk_2);
[download]

$yuk_1:
SV = NULL(0x0) at 0x814eacc
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY)
$yuk_2:
SV = RV(0x8158458) at 0x814eae4
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,ROK)
  RV = 0x814490c
  SV = PVHV(0x8153550) at 0x814490c
    REFCNT = 1
    FLAGS = (SHAREKEYS)
    IV = 0
    NV = 0
    ARRAY = 0x0
    KEYS = 0
    FILL = 0   
    MAX = 7
    RITER = -1
    EITER = 0x0

Abigail