./perl/problems.txt

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Array-Referenzen werden zu Hashreferenzen

  DB<50> @arr=(0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15)

  DB<69> x \{@arr}
0  SCALAR(0x91a4a94)
   -> HASH(0x91a198c)
      0 => 1
      10 => 11
      12 => 13
      14 => 15
      2 => 3
      4 => 5
      6 => 7
      8 => 9
  DB<70> x \@arr    # this way it works as expected
0  ARRAY(0x919d7e4)
   0  0
   1  1
   2  2
   3  3
   4  4
   5  5
   6  6
   7  7
   8  8
   9  9
   10  10
   11  11
   12  12
   13  13
   14  14
   15  15
  DB<71> x {@arr}


  DB<66> $cpy= \{@arr[10..12]}

  DB<67> x $cpy
0  SCALAR(0x91a29cc)
   -> HASH(0x91a2b70)
      10 => 11
      12 => undef
  DB<68> x $cpy->[0]
Not an ARRAY reference at (eval 89)[/usr/local/lib/perl5/5.6.0/perl5db.pl:1510] line 2, <IN> line 72.


How are slices implemented? Full-blown arrays created as (shallow)
copies of the specified section of the original array, or just a
pointer to the original array, plus two indizes?


  DB<75> $deepobj=[30,40,50,60]

  DB<76> 
main::(./tv_gui_regrtest.pl:61):	print "ALL TESTS SUCCESFUL.\n";
  DB<76> 
ALL TESTS SUCCESFUL.
Debugged program terminated.  Use q to quit or R to restart,
  use O inhibit_exit to avoid stopping after program termination,
  h q, h R or h O to get additional info.  
  DB<76> x $deepobj
0  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
  DB<77> push @arr, $deepobj

  DB<78> push @arr, 42

  DB<79> push @arr, 43
  DB<80> x @arr
0  0
1  1
2  2
3  3
4  4
5  5
6  6
7  7
8  8
9  9
10  10
11  11
12  12
13  13
14  14
15  15
16  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
17  42
18  43

  DB<82> x @cpy2=@arr[13..17]
0  13
1  14
2  15
3  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
4  42
  DB<83> x push @$cpy2[2],70
Type of arg 1 to push must be array (not array slice) at (eval 104)[/usr/local/lib/perl5/5.6.0/perl5db.pl:1510] line 2, at EOF
  DB<84> x push @{$cpy2[2]},70
0  1
  DB<85> x @cpy2
0  13
1  14
2  15
3  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
4  42
  DB<86> x push @{$cpy2[3]},70
0  5
  DB<87> x @cpy2
0  13
1  14
2  15
3  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
   4  70
4  42
  DB<88> x @arr
0  0
1  1
2  2
3  3
4  4
5  5
6  6
7  7
8  8
9  9
10  10
11  11
12  12
13  13
14  14
15  15
16  ARRAY(0x91a6bac)
   0  30
   1  40
   2  50
   3  60
   4  70
17  42
18  43
  DB<89> 

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Apparently "iterators" over arrays as established by e.g. "foreach"
are not part of the array itself:

  DB<89> @arr2=(0,1,2)

  DB<91> for $it1 (@arr2) { for $it2 (@arr2) { print "$it1 $it2   "; }}
0 0   0 1   0 2   1 0   1 1   1 2   2 0   2 1   2 2   

Is there a way to create and increment such iterators manually, or are
they an integrated part of the "foreach" magic?

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how do you obtain a reference to a hash returned by a function call?

e.g.:

this gives me the hash returned by "map":

  DB<126> x map { ($_=>1) } 6,8,3,4,2
0  6
1  1
2  8
3  1
4  3
5  1
6  4
7  1
8  2
9  1

same here (why doesn't this create a reference to the hash?)

  DB<127> x { map { ($_=>1) } 6,8,3,4,2 }
0  6
1  1
2  8
3  1
4  3
5  1
6  4
7  1
8  2
9  1

but this gives me a reference to a reference to the hash!

  DB<128> x \{ map { ($_=>1) } 6,8,3,4,2 }
0  REF(0x84dfb90)
   -> HASH(0x84dc22c)
      2 => 1
      3 => 1
      4 => 1
      6 => 1
      8 => 1

And this doesn't work either:

  DB<129> x \ map { ($_=>1) } 6,8,3,4,2
0  SCALAR(0x84e0a98)
   -> 6
1  SCALAR(0x84dc250)
   -> 1
2  SCALAR(0x84e4254)
   -> 8
3  SCALAR(0x84de0cc)
   -> 1
4  SCALAR(0x84e0b64)
   -> 3
5  SCALAR(0x84e0d7c)
   -> 1
6  SCALAR(0x84e0a74)
   -> 4
7  SCALAR(0x84e4278)
   -> 1
8  SCALAR(0x84dc004)
   -> 2
9  SCALAR(0x84de1a4)
   -> 1
  DB<130> 

it only works as expected when I create a temporary variable:

  DB<130> x %res=map { ($_=>1) } 6,8,3,4,2; \%res
0  HASH(0x84e0c54)
   2 => 1
   3 => 1
   4 => 1
   6 => 1
   8 => 1
  DB<131> 

aaaah...

  DB<141> x +{ map {$_+3} 6,8,3,4,2,5 }
0  HASH(0x84e0cb4)
   5 => 8
   6 => 7
   9 => 11
  DB<142> 

(see "man perlref"/"making references"/3.)
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