Far too often I find myself having to check a bunch of input args for definedness. It's annoying, and this annoyance is almost definitely the reason for defined-or in Perl 5.10. However, I need a solution that works in older perls.

I came up with an idea that seems to work, but it works by messing about with @_. This makes me nervous. Anyone care to tell me why this code is dangerous?

I've got two routines to munge @_. One changes the source array, called fix_undef(), which seems like bad news to me. The other, called no_sfx_fix_undef() seems to be safe.

So, as far as my limited brain can tell, the second function is safe to use unless I plan on using @_ to modify the original routine's arguments. Any other gotchas I should know about? 

use strict;
use warnings;

my @args = ( qw/fee fie foe fum/, undef, 1..3 );

print "No SFX\n", '-'x10, "\n";
Sub_With_NO_Side_Effects( @args );

print map { "'$_'\n" } @args;

print "\nSFX\n", '-'x10, "\n";
Sub_With_Side_Effects( @args );

print map { "'$_'\n" } @args;

sub Sub_With_NO_Side_Effects {
    &no_sfx_fix_undef;
    print "$_: '$_[$_]'\n" foreach  0..$#_;
}

sub Sub_With_Side_Effects {
    &fix_undef;
    print "$_: '$_[$_]'\n" foreach  0..$#_;
}

# This sub modifies the original calling function's variables.  BAD NE
+WS
sub fix_undef {
    defined $_ or $_ = '' foreach @_;
}

# This seems to be ok...
sub no_sfx_fix_undef {
    @_ = map { defined $_ ? $_ : '' } @_;
}
__END__ # OUTPUT

No SFX
----------
0: 'fee'
1: 'fie'
2: 'foe'
3: 'fum'
4: ''
5: '1'
6: '2'
7: '3'
Use of uninitialized value in concatenation (.) or string at C:\temp\t
+est.pl line 9.
'fee'
'fie'
'foe'
'fum'
''
'1'
'2'
'3'

SFX
----------
0: 'fee'
1: 'fie'
2: 'foe'
3: 'fum'
4: ''
5: '1'
6: '2'
7: '3'
'fee'
'fie'
'foe'
'fum'
''
'1'
'2'
'3'

[download]


TGI says moo

In reply to Messing with @_ by TGI

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