sub initialize_with_pars {
    my $self = shift;

# Alternative 1: a,b can be overwritten by AVPs given in @_
    %{$self} = (%{$self},       'a' => 10 , 'b' => 20,  @_); 

# Alternative 2: init. of a,b has priority over AVPs from @_
#   %{$self} = (%{$self},  @_,  'a' => 10 , 'b' => 20);

}

...
# Usage:
$self->initialize_with_pars;
# or
$self->initialize_with_pars( 'c' => 30 );