Perl Best Practices中一个缺省参数的例子

直接贴代码，忘了时看看，尤其是红色的部分。

  
    

   
     
   
      1 
   
      Readonly 
   
     my
   
      
   
     %PAD_DEFAULTS
   
      
   
     =>
   
      (

   
      2 
   
      cols 
   
     =>
   
      
   
     78
   
     ,
   
     

   
      3 
   
      centered 
   
     =>
   
      
   
     0
   
     ,
   
     

   
      4 
   
      filler 
   
     =>
   
      
   
     $SPACE
   
     ,
   
     

   
      5 
   
      
   
     #
   
      etc.
   
     

   
      6 
   
      
   
      );

   
      7 
   
     

   
      8 
   
      
   
     sub
   
      padded {

   
      9 
   
      
   
     my
   
      (
   
     $text
   
     ,
   
      
   
     $arg_ref
   
     ) 
   
     =
   
      
   
     @_
   
     ;

   
     10 
   
     

   
     11 
   
      
   
     #
   
      Unpack optional arguments and set defaults...
   
     

   
     12 my %arg = ref $arg_ref eq 'HASH' ? (%PAD_DEFAULTS, %{$arg_ref})
13 : %PAD_DEFAULTS
   
     ;

   
     14 
   
     

   
     15 
   
      
   
     #
   
      Compute left and right spacings...
   
     

   
     16 
   
      
   
      
   
     my
   
      
   
     $gap
   
      
   
     =
   
      
   
     $arg
   
     {cols} 
   
     -
   
      
   
     length
   
      
   
     $text
   
     ;

   
     17 
   
      
   
     my
   
      
   
     $left
   
      
   
     =
   
      
   
     $arg
   
     {centered} 
   
     ?
   
      
   
     int
   
     (
   
     $gap
   
     /
   
     2
   
     ) 
   
     :
   
      
   
     0
   
     ;

   
     18 
   
      
   
     my
   
      
   
     $right
   
      
   
     =
   
      
   
     $gap
   
      
   
     -
   
      
   
     $left
   
     ;

   
     19 
   
     

   
     20 
   
      
   
     #
   
      Prepend and append space...
   
     

   
     21 
   
      
   
      
   
     return
   
      
   
     $arg
   
     {filler} x 
   
     $left
   
      
   
     .
   
      
   
     $text
   
      
   
     .
   
      
   
     $arg
   
     {filler} x 
   
     $right
   
     ;

   
     22 
   
      }