perldata - Perl Data Types

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(Continued from previous part...)

Scalar Object Interpretations

When a scalar object is used in an operation, it could be interpreted in three ways depending on the type of value the operation is expecting:

• A number, if the operation is expecting a numeric value. If the content in the object is a string, Perl will try to parse it into a number. If parsing failed, it will be interpreted as 0.
• A string, if the operation is expecting a string value. If the content in the object is a number, Perl will convert it into a string representation of that number.
• A TRUE or FALSE, if the operation is expecting a boolean value. Perl will interpret number 0, string '0', and empty string '' as FALSE, and anything else as TRUE.

To verify the rules listed above, I wrote the following program:

#- ScalarObject.pl
#- Copyright (c) 1995 by Dr. Herong Yang
#
   print(0.00, "\n");                  # 0
   print(00.00, "\n");                 # 00
   print(1e-1, "\n");                  # 0.1
   print(1e+50, "\n");                 # 1e+050
   print(1e+100, "\n");                # 1e+100
   print(1e+1000, "\n");               # 1.#INF
   print(1e+1000 + 1, "\n");           # 1.#INF
   print('1e+1000' + 1, "\n");         # 1.#INF
   print(0.1234567890123456789, "\n"); # 0.123456789012346
   print(1 / 3, "\n");                 # 0.333333333333333
   print(1 / '3', "\n");               # 0.333333333333333
   print(1 + 3, "\n");                 # 4                
   print(1.3, "\n");                   # 1.3              
   print(1 . 3, "\n");                 # 13               
   print((1 . 3) * 5, "\n");           # 65               
   print('Hello '. 'world!', "\n");    # Hello world!     
   print(1 + 'a', "\n");               # 1                
   print(1 * 'a', "\n");               # 0                
   print(1 + '', "\n");                # 1                
   print('FALSE', "\n") if (not 0);    # FALSE            
   print('FALSE', "\n") if (not '0');  # FALSE            
   print('FALSE', "\n") if (not '');   # FALSE            
   print('TURE', "\n") if (' ');       # TURE             
   print('TURE', "\n") if (1);         # TURE             

The outputted values are entered into the program as comments. You are probably surprised to see some of the outputted values. Me too.

If a scalar variable is used in an operation, its assigned object will be interpreted and used in the operation. But if a scalar variable is not assigned (undefined), it will be interpreted as:

• 0, if a numerical value is expected.
• '', if a string value is expected.
• FALSE, if a boolean value is expected.

Here is a program to show you how a undefined scalar variable behaves in an operation:

#- undefined.pl
#- Copyright (c) 1995 by Dr. Herong Yang
#
   print '(' . $a . ')', "\n";
   print 1 + $a, "\n";
   print 1 * $a, "\n";
   print 'FALSE', "\n" if (not $a);

(Continued on next part...)

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