Safe list assignment

Perl's list assignment feature is very useful.

    sub returns_three_things { return (1, 2, 3) }
    my ($x, $y, $z) = returns_three_things();

Often, though, you want to add some error checking.  Particularly when providing
an interface that others can call.

    # Parameters: first name, last name, birthday.
    sub print_person_details {
       croak 'pass three arguments' if @_ != 3;
       my ($first_name, $last_name, $birthday) = @_;
       say "$first_name $last_name was born on $birthday";
    }

The extra 'croak' test gives a more friendly error message than 'use of
uninitialized value in ...', which would require the user of the subroutine to
go digging in its code to find what he passed wrongly.

Even in code that's not part of a public interface, you may want to check that
the list has the right size before you do the assignment, just to catch
programmer mistakes early rather than waiting for an uninitialized value warning
later on.

But it's rather a pain to keep checking the list size each time.  When you
'unpack a tuple' in Python the size is checked and an exception is thrown if
it's too big or too small.  Is there an equivalent in Perl?  Something like

     safe_assign ($a, $b, $c) = @array;    # will die if scalar(@array) != 3

-- 
Ed Avis <[email protected]>