Concept map of data types

[programmer.perl]

Hi Monks!

I'm getting confused on data types, especially on complex data types with a references. To the Perl enthusiast, like me, it take a bit of time to memorize all data combinations in Perl. Therefore, to understand better, I gathered formats of a data types from a book (Perl by Example 4th edit.). It would be better if you look to this with your 'eagle' eye, every-time, Master has something to say to a beginner concerning his works..., maybe this concept map needs to be filled with additional FORMATs that I don't know... I attached the text as a code, otherwise some symbols were interpolating...

Thanks to all monks (especially to 2teez, Marshall, aitap) who helped in redesigning this map. This is a latest view:

---PERL DATA TYPES---

COMPLEX DATA TYPES
# We just need to memorize that arrays and hashes can contain
# only scalars and references, and in order to use contents of 
# an object by its reference you need ->.

@abc=([],);               LIST OF LISTS

@abc=({""=>"",},);        ARRAY OF HASHES

$ref=['',['',]];          LIST OF LISTS: anonymous arrays

$ref=['',];               ANONYMOUS ARRAYS

$ref=[{""=>"",},];        ANONYMOUS ARRAY OF HASHES

%abc=(""=>"",);           HASH

%abc=(""=>{""=>"",},);    HASHES OF HASHES 

%abc=(""=>["",]);         HASHES OF HASHES

$ref={""=>"",};           ANONYMOUS HASHES

$ref={key=>{""=>"",},};   ANONYMOUS HASH OF HASHES

$ref={""=>{""=>['',]},};  HASH OF HASHES WITH LISTS OF VALUES

-----------------------------------------------------------

  --DETAILS--

SCALAR-$
$abc = "string";
$abc = 12;
$abc = $def;

------------------------------------------------------------

ARRAY-@
@abc = "q, w, e, r, t, y";
@abc = (1, 2, 3, 4, 5, 6);
____________________________________________________________
LIST OF LISTS--FORMAT: @abc=([],);
my @array = ( # "(...)" means array
 [ 1, 2, 3 ], # "[...]" means array reference
 [ 4, 5, 6 ],  );
print $array[1]->[2]; # output: 6
# firstly, we get the second element from the array
# secondly, it's a reference to an array, so we add "->" and 
# get the third element of it

my @abc =  #abc is an array of references to arrays
(   [ qw (q   w  e  r)  ],
    [ qw (1   x  3  r)  ],
    [ qw (qwe rt 434 )  ],  );

foreach my $array_ref (@abc)
{  print "@$array_ref \t";
   print "third element: \t", $array_ref->[2],"\n"; }

__END__
Prints:
q w e r     third element:  e
1 x 3 r     third element:  3
qwe rt 434  third element:  434
____________________________________________________________
ARRAY OF HASHES--FORMAT: @abc=({""=>"",},);
@abc = ({"key"=>"val", "key"=>val,},);
print $abc[0]->{"key"};
____________________________________________________________
LIST OF LISTS: anonymous arrays--FORMAT: $ref=['',['',]];
my $ref = ['1', '2', ['a', 'b']];
print $ref->[0]; output: 1
print $ref->[2]->[1]; # output: b
print @{$ref}; # output: 1 2 ARRAY(0x8a6f134)
print @{$ref-[2]}; # output: a b
____________________________________________________________
ANONYMOUS ARRAYS--FORMAT: $ref=['',];
my $ref = ['a', 'b',];
print "$ref->[0]"; # or $$ref[0] or ${$ref}[0], output: a
print "@{$ref}"; # output: a b
____________________________________________________________
ANONYMOUS ARRAY OF HASHES--FORMAT: $ref=[{""=>"",},];
my $ref = [{"keyA"=>"valA",},];
print "$ref->[0]->{keyA}"; # output: valA
push @{$ref}, {"keyC"=>"valC",};
while (($k,$v)=each %{$ref->[1]}) {print "$k -- $v";}

------------------------------------------------------------

HASH-%
FORMAT: %abc=(""=>"",);
%abc=("key1"=>"val1", "key2"=>val2,);
print "$abc{'key2'}"; # output: val2
____________________________________________________________
HASHES OF HASHES
A) FORMAT: %abc=(""=>{""=>"",},);
%abc = ("key1"=>{"key1-1"=>"valueAA", "key1-2"=>"valueAB"},);
print qq/$abc{key1}->{key1-2}/; # output: valueAB

B) FORMAT: %abc=(""=>["",]);
%abc = ("key"=>["val", vals,]);
print "$abc{key}->[1]"; # output: vals
____________________________________________________________
ANONYMOUS HASHES--FORMAT: $ref={""=>"",};
my $ref = {"key"=>"val",};
print $ref->{"key"};
print keys %$ref; # or values %$ref, output: key or val
____________________________________________________________
ANONYMOUS HASH OF HASHES--FORMAT $ref={key=>{""=>"",},};
my $ref = {key1=>{"key"=>"val", "key"=>val,},};
print "$ref->{'key1'}->{'key'}";
$ref->{'key1'}->{'key'}=val;
print %{$ref->{'key1'}}; # output: keyvalkeyval
foreach $outer_key (keys %{$ref}) { 
    print "Outer key: $outer_key\n";
    while (($k,$v)=each(%{$ref->{$k}})) {print "$k: $v"} }
____________________________________________________________
HASH OF HASHES WITH LISTS OF VALUES--FORMAT: $ref={""=>{""=>['',]},};
my $ref = {"key1"=>{"key"=>['a','b',]}, "key2"=>{"key"=>['c','d',]},};
print $ref->{"key1"}->{"key"}->[0]; # output: a
print "@{$ref->{'key2'}->{'key'}}"; # output: c d
push @{$ref->{'key1'}->{'key2'}}, "@{$adds}"; 
             # anonymous array: $adds = ["e","f"];
print "@{$ref->{'key2'}->{'key'}}"; # output: c d e f

-------------------------------------

# "[ ITEMS ]" makes a new, anonymous array, and returns a 
# reference to that array.  "{ ITEMS }" makes a new, anonymous 
# hash, and returns a reference to that hash.

# References are documented in perlref and perlreftut.  
# Examples of complex data structures are given in perldsc and perllol
# Examples of structures and object-oriented classes are in perltoot.