Re^6: Prototype for constant items???

You can't expect to tell the difference between the size of an array (such as '3'), and a plain old number (such as '3').

Again: I can tell the difference between scalar and an array, but just not for constants.

You're still missing the point ... I marked it for you, to make it clearer:

  DB<4> sub tst (\[$@]) { print ref $_[0] }
  
  DB<5> $a="a";@a=(1..3)
  
  DB<6> tst $a
SCALAR
  DB<7> tst @a
ARRAY
  DB<8> tst "a"   # <--------- that's the point !
Type of arg 1 to main::tst must be one of [$@] (not constant item) at 
+(eval 12)[/usr/share/perl/5.10/perl5db.pl:638] line 2, at EOF
[download]

Cheers Rolf

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Re^7: Prototype for constant items??? by SuicideJunkie (Vicar) on Sep 28, 2009 at 13:53 UTC
The problem there, is that you are still using prototypes. I am saying; ditch that, and just check the parameters in the sub. If the caller wants to pass an array as the first parameter, they can throw a reference slash in front of it, or square brackets around it. If they want to pass a list of multiple parameters, they can just pop the ($alpha,@rgb) in there without your sub forcing it into just two parameters and then trying to untangle it later. My main point: Use prototypes if you want to mangle the caller's code. Use `if` `croak`, `warn`, etc if you want to do type and sanity checking. Note: If they pass an array where they should have passed an arrayRef, then you should `croak` with a detailed version of "Too Many Parameters!" and/or "Value out of range", where applicable. Come to think of it, it would be nice to have a template of: `sub foo { my $failed; ($failed = 1 and carp "First Parameter must be greater than zero") i +f $_[0] <= 0; ($failed = 1 and carp "Too many parameters") if scalar @_ > 3; die "Invalid parameters; cannot continue" if $failed; ... }` [download] since that would print out all of the errors before stopping, rather than just one error per run. - SJ How to make perldoc.perl.org resizable too!	[reply] [d/l] [select]

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Re^7: Prototype for constant items???
by SuicideJunkie (Vicar) on Sep 28, 2009 at 13:53 UTC

The problem there, is that you are still using prototypes. I am saying; ditch that, and just check the parameters in the sub.

If the caller wants to pass an array as the first parameter, they can throw a reference slash in front of it, or square brackets around it. If they want to pass a list of multiple parameters, they can just pop the ($alpha,@rgb) in there without your sub forcing it into just two parameters and then trying to untangle it later.

My main point: Use prototypes if you want to mangle the caller's code. Use if croak, warn, etc if you want to do type and sanity checking.

Note: If they pass an array where they should have passed an arrayRef, then you should croak with a detailed version of "Too Many Parameters!" and/or "Value out of range", where applicable.

Come to think of it, it would be nice to have a template of:

sub foo
{
  my $failed;
  ($failed = 1 and carp "First Parameter must be greater than zero") i
+f $_[0] <= 0;
  ($failed = 1 and carp "Too many parameters") if scalar @_ > 3;

  die "Invalid parameters; cannot continue" if $failed;
  ...
}
[download]

- SJ

How to make perldoc.perl.org resizable too!

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