use constant UNDEFINED_SUBROUTINE_ERROR => do {
    eval {
        no strict 'refs';    ## no critic NoStrict
        &{'---'};
    };
    my $e = $@;

    # Undefined subroutine &main::--- called at .../Primitives.pm line 12.
    my ($msg) = $e =~ / \A
                        (.+)    # 'Undefined subroutine'
                        (?<=\s) # ' '
                        \S*     # &main::
                        ---/mx
        or die q[Perl's error message changed! Damn! Fix this regex.];

    $msg;
};

sub ... {
    ...
    # If the error is that I couldn't call the
    # function because it didn't exist or AUTOLOAD wouldn't DWIM then
    # I want to return fail.
    #
    # I want to avoid Class::Delegation's misfeature of eating all
    # non-related errors while it traps for the few things that it
    # needs.
    if ( my $e = $@ ) {

        # Extreme caution here.
        if ( $e =~ UNDEFINED_SUBROUTINE_ERROR ) {
            return FAIL;
        }
        elsif ( defined blessed $e ) {

            # Rethrow exception objects...
            die $e;
        }
        else {

            # Rethrow exception strings...
            if ( not $e = /\n\z/ ) {
                $e .= "\n";
            }
            die $e;
        }
    }
    ...
}