Re^2: RFC: New style for argument check in subs

[LanX]

As I already said, accepting undef as valid argument is such a special and rare case that it should be covered by another approach. (see footnotes in OP)

Here using ternaries is far more explicit and shows that a special argument undef is accepted.

my $a = exists $arg{a} ? $arg{a} : 'else case';

But I agree that it's better to name the error die('Undefined argument!') instead of 'Missing argument' to avoid such misunderstandings.

[Tux]

Not rare at all! Both as unnamed and as named parameter used in DBI + DBD::CSV:

use DBI;
my $dbh = DBI->connect (
    "dbi:CSV",                  # Unnamed, driver
    undef,                      # Unnamed, username
    undef,                      # Unnamed, password
    {   f_ext    => ".csv/r",   # Named and defined
        f_schema => undef,      # Named and undefined
        });

FWIW all NULL values in a database are refered to through undef, so you'll see a lot of those in both named and unnamed arguments to functions and methods.

[LanX]

Good point.

But in those cases checks for existence should be explicit.

UPDATE: You convinced me that

*** Unpack Named First

is a danegrous option. Thanks :)