sub new {
 
    # parameters:
    # [$this],
    # @attributes: tree, messageNum, messageText
    
    my ($this, @attributes) = @_;

    # "process" optional attributes
    my %attributes = (
        tree => undef,
        messageNum => undef,
        messageText => undef,
        @attributes,
    );

    # assert for valid argument list
    if ((keys %attributes) > 3) {
        die "invalid argument list during function call!\n";
    }

    # assert mandatory parameters
    my $tree = $attributes{tree};
    my $messageNum = $attributes{messageNum};
    my $messageText = $attributes{messageText};
    if ((!defined($this)) || (!defined($tree)) || (!defined($messageNum))) {
        die "invalid argument list during function call!\n";
    }

##</code><code>##


sub new {
 
    # parameters:
    # [$this],
    # @namedParameters: tree, messageNum, (messageText)
    
    ##### process parameters #####

    my ($this, @namedParameters) = @_;

    # process named parameters (with default values)
    my ($tree, $messageNum, $messageText) = assertNamedParameters([
        numNamedParameters => 3,
        tree => undef,
        messageNum => undef,
        messageText => undef,
        ], \@namedParameters
    );

    # check mandatory paramters
    assertValueIsDefined($this, $tree, $messageNum);

##</code><code>##

sub assertNamedParameters {
 
    # parameters:
    # $parametersRef, $argumentsRef
    
    my ($parametersRef, $argumentsRef) = @_;
    
    # check passed arguments
    assertValueIsDefined($parametersRef, $argumentsRef);
    
    # create parameter hash
    my %parameters = (
        @{$parametersRef},
        @{$argumentsRef},
    );
    
    # get valid number of parameters
    if (!exists($parameters{numNamedParameters})) {
        assertThrowException(
            "parameter key ('numNamedParameters') has not 
             been defined in passed parameter hash");   
    }

    # get number of parameters
    my $numNamedParameters = $parameters{numNamedParameters};
        
    # assert for valid parameter count
    if ($numNamedParameters < 1) {
        assertThrowException(
            "invalid number of parameters ($numNamedParameters) specified
             (minimum is one parameter)");
    }

    # assert parameter list for valid parameter count
    # (account for the numParameters key itself (!))
    if ((keys %parameters) != ($numNamedParameters + 1)) {
        assertThrowException(
            "invalid number of parameters ($numNamedParameters) passed");
    }

    # return parameter values
    my ($parameterName, $parameterValue, @parameterValues);

    # retrieve each given parameter
    # (skipping 'numParameters' key)
    for (my $i = 1; $i <= $numNamedParameters; $i++) {

        # retrieve parameter name from parameter list
        # IN ORDER concerning given parameter list!
        $parameterName = $parametersRef->[2*$i];

        # get parameter value from parameter hash
        $parameterValue = $parameters{$parameterName};
        push(@parameterValues, $parameterValue);
    }

    return(@parameterValues);
}