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Section 9.2.  Homonyms

 
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9.2. Homonyms

Don't give subroutines the same names as built-in functions.

If you declare a subroutine with the same name as a built-in function, subsequent invocations of that name will still call the builtin...except when occasionally they don't. For example:

    sub lock {
        my ($file) = @_;
        return flock $file, LOCK_SH;
    }

    sub link {
        my ($text, $url) = @_;
        return qq{<a href="$url">$text</a>};
    }

    lock($file);                   # Calls 'lock' subroutine; built-in 'lock' hidden
    print link($text, $text_url);  # Calls built-in 'link'; 'link' subroutine hidden

Perl considers some of its builtins (like link) to be "more built-in" than others (like lock), and chooses accordingly whether to call your subroutine of the same name. If the builtin is "strongly built-in", an ambiguous call will invoke it, in preference to any subroutine of the same name. On the other hand, if the builtin is "weakly built-in", an ambiguous call will invoke the subroutine of the same name instead.

Even if these subroutines did always work as expected, it's simply too hard to maintain code where the program-specific subroutines and the language's keywords overlap:

    sub crypt { return "You're in the tomb of @_\n"   }
    sub map   { return "You have found a map of @_\n" }
    sub chop  { return "You have chopped @_\n"        }
    sub close { return "The @_ is now closed\n"       }
    sub hex   { return "A hex has been cast on @_\n"  }

    print crypt( qw( Vlad Tsepes ) );             # Subroutine or builtin?

    for my $reward (qw( treasure danger) ) {
         print map($reward, 'in', $location);     # Subroutine or builtin?
    }

    print hex('the Demon');                       # Subroutine or builtin?
    print chop('the Demon');                      # Subroutine or builtin?

There is an inexhaustible supply of subroutine names available; names that are more descriptive and unambiguous. Use them:


    sub in_crypt  { return "You're in the tomb of @_\n"   }
    sub find_map  { return "You have found a map of @_\n" }
    sub chop_at   { return "You have chopped @_\n"        }
    sub close_the { return "The @_ is now closed\n"       }
    sub hex_upon  { return "A hex has been cast on @_\n"  }

    print in_crypt( qw( Vlad Tsepes ) );

    for my $reward (qw( treasure danger )) {
        print find_map($reward, 'in', $location);
    }

    print hex_upon('the Demon');
    print chop_at('the Demon');

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