I also did some testing with ActiveState Perl 5.6.1

If you use the flipflopped var in a string, and if there is a space (any whitespace) immediately following the flipflop variable, then it will be flipped twice.

I also tested if concatenating a space causes the same problem (not shown in test code below) and it did not.

Examples:
$f="$flipflop "; doesn't work.
$f="$flipflop\n"; doesn't work.
$f="$flipflop"; works
$f="{$flipflop}_xxx "; works
$f="\n$flipflop"; works

To test this, I modified the tie::flipflop module to print Doing a fetch, with state... everytime the state is flipped.

Note: I used readmore tags around the code and results, but I can't see if they are really working until I create my post. so if they are not, I apologize.

My test script is below 

use myFlipFlop;

# original OP code
tie my $flipflop => Tie::FlipFlop => ( 'white', 'black' );

print "="x10,"\n";
print "Original OP Code\n";
print "="x10,"\n";
print qq|$flipflop\n|;
print qq|$flipflop\n|;
print qq|$flipflop\n|;
print qq|$flipflop\n|;

# my tests.
# Thought #1, perl optimizes 'print "$a$b"' by concatenating $a.$b.

# First, remove the 'printing part' and see what happens

  # is it related to concatenating strings?
  print "\n\n","="x10,"\n";
  print "Non-White space after flipflop var\n",
        "but white space at end of string\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  my $start = "$flipflop";
  print "Setting \$one\n";
  my $one = "{$flipflop}_one ";
  print "Setting \$two\n";
  my $two = "($flipflop}_two_two ";
  print "Setting \$three\n";
  my $three = "{$flipflop}_three_three_three ";

  print "\n\nstart:\t$start\n",
             "one:\t$one\n",
             "two:\t$two\n",
             "three:\t$three\n";
  # Result: all of the aboved worked.

  # is it related to concatenating strings?
  print "\n\n","="x10,"\n";
  print "White space immediately after flipflop var\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  my $start = "$flipflop";
  print "Setting \$one\n";
  my $one = "$flipflop one ";
  print "Setting \$two\n";
  my $two = "$flipflop two two ";
  print "Setting \$three\n";
  my $three = "$flipflop three three three ";

  print "\n\nstart:\t$start\n",
             "one:\t$one\n",
             "two:\t$two\n",
             "three:\t$three\n";
  # Result: all of the aboved worked.


  # try multiple \n
  # i.e. does each \n cause it to flip?
  print "\n\n","="x10,"\n";
  print "Using multiple '\\n' immediately after var \n";
  print "="x10,"\n";

  print "Setting \$start\n";
  $start = "$flipflop";
  print "Setting \$one\n";
  $one = "$flipflop\n";
  print "Setting \$two\n";
  $two = "$flipflop\n\n";
  print "Setting \$three\n";
  $three = "$flipflop\n\n\n";

  print "\n\nstart:\t$start\n",
            "one:\t$one",
            "two:\t$two",
            "three:\t$three";
  # RESULT: Each flipped twice.

  # try multiple \n
  # i.e. does each \n cause it to flip?
  print "\n\n","="x10,"\n";
  print "Using multiple '\\n', but not immedieately after flipflop\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  $start = "$flipflop";
  print "Setting \$one\n";
  $one = "{$flipflop}_one\n";
  print "Setting \$two\n";
  $two = "{$flipflop}_two_two\n\n";
  print "Setting \$three\n";
  $three = "{$flipflop}_three_three_three\n\n\n";

  print "\n\nstart:\t$start\n",
            "one:\t$one",
            "two:\t$two",
            "three:\t$three";

  # RESULT: Each flipped twice.

  # try multiple \t
  # i.e. does each \t cause it to flip?
  print "\n\n","="x10,"\n";
  print "Using multiple '\\t'  (one on one, two on two, etc)\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  $start = "$flipflop";
  print "Setting \$one\n";
  $one = "$flipflop\t";
  print "Setting \$two\n";
  $two = "$flipflop\t\t";
  print "Setting \$three\n";
  $three = "$flipflop\t\t\t";

  print "\n\nstart:\t$start\n",
            "one:\t$one\n",
            "two:\t$two\n",
            "three:\t$three\n";
  # RESULT: Each flipped twice.
  # RESULT: Same as above.


  # How about at the beginning of the var?
  # i.e. does each something at begining cause it to flip?
  print "\n\n","="x10,"\n";
  print "Using something a beginning of var\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  $start = "$flipflop";
  print "Setting \$one\n";
  $one = "one $flipflop";
  print "Setting \$two\n";
  $two = "two two $flipflop";
  print "Setting \$three\n";
  $three = "three three three $flipflop";

  print "\n\nstart:\t$start\n",
            "one:\t$one\n",
            "two:\t$two\n",
            "three:\t$three\n";
  # How about at the beginning of the var?
  # i.e. does each \n cause it to flip?
  print "\n\n","="x10,"\n";
  print "Using multiple '\\n' at beginning of var\n",
        "  (one on one, two on two, etc)\n";
  print "="x10,"\n";

  print "Setting \$start\n";
  $start = "$flipflop";
  print "Setting \$one\n";
  $one = "\n$flipflop";
  print "Setting \$two\n";
  $two = "\n\n$flipflop";
  print "Setting \$three\n";
  $three = "\n\n\n$flipflop";

  print "\n\nstart:\t$start\n",
            "one:\t$one\n",
            "two:\t$two\n",
            "three:\t$three\n";

#RESULT: Works fine
  exit;

[download]
and the results are below 
Using Sandy's version
==========
Original OP Code
==========
Doing a fetch, with state black white
Doing a fetch, with state white black
black
Doing a fetch, with state black white
Doing a fetch, with state white black
black
Doing a fetch, with state black white
Doing a fetch, with state white black
black
Doing a fetch, with state black white
Doing a fetch, with state white black
black


==========
Non-White space after flipflop var
but white space at end of string
==========
Setting $start
Doing a fetch, with state black white
Setting $one
Doing a fetch, with state white black
Setting $two
Doing a fetch, with state black white
Setting $three
Doing a fetch, with state white black


start:  white
one:    {black}_one 
two:    (white}_two_two 
three:  {black}_three_three_three 


==========
White space immediately after flipflop var
==========
Setting $start
Doing a fetch, with state black white
Setting $one
Doing a fetch, with state white black
Doing a fetch, with state black white
Setting $two
Doing a fetch, with state white black
Doing a fetch, with state black white
Setting $three
Doing a fetch, with state white black
Doing a fetch, with state black white


start:  white
one:    white one 
two:    white two two 
three:  white three three three 


==========
Using multiple '\n' immediately after var 
==========
Setting $start
Doing a fetch, with state white black
Setting $one
Doing a fetch, with state black white
Doing a fetch, with state white black
Setting $two
Doing a fetch, with state black white
Doing a fetch, with state white black
Setting $three
Doing a fetch, with state black white
Doing a fetch, with state white black


start:  black
one:    black
two:    black

three:  black




==========
Using multiple '\n', but not immedieately after flipflop
==========
Setting $start
Doing a fetch, with state black white
Setting $one
Doing a fetch, with state white black
Setting $two
Doing a fetch, with state black white
Setting $three
Doing a fetch, with state white black


start:  white
one:    {black}_one
two:    {white}_two_two

three:  {black}_three_three_three




==========
Using multiple '\t'  (one on one, two on two, etc)
==========
Setting $start
Doing a fetch, with state black white
Setting $one
Doing a fetch, with state white black
Doing a fetch, with state black white
Setting $two
Doing a fetch, with state white black
Doing a fetch, with state black white
Setting $three
Doing a fetch, with state white black
Doing a fetch, with state black white


start:  white
one:    white   
two:    white           
three:  white                   


==========
Using something a beginning of var
==========
Setting $start
Doing a fetch, with state white black
Setting $one
Doing a fetch, with state black white
Setting $two
Doing a fetch, with state white black
Setting $three
Doing a fetch, with state black white


start:  black
one:    one white
two:    two two black
three:  three three three white


==========
Using multiple '\n' at beginning of var
  (one on one, two on two, etc)
==========
Setting $start
Doing a fetch, with state white black
Setting $one
Doing a fetch, with state black white
Setting $two
Doing a fetch, with state white black
Setting $three
Doing a fetch, with state black white


start:  black
one:    
white
two:    

black
three:  


white

[download]
UPDATE: Just added a little example at beginning of post.

QUESTION:

Is the FETCH method called twice for all tied objects, in the conditions noted above?

My curiosity is truly peaked. Since I have no real experience 'tieing' anything, it would take some time for me to test. Maybe someone else would be willing?...

In reply to Re: FETCHing twice in Tie::FlipFlop by Sandy
in thread FETCHing twice in Tie::FlipFlop by CharlesClarkson

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