/*!

\page named-param Named Parameters

\section named-func-param Named "Function" Parameters

C++ makes it possible to use default parameter values when calling a

function. In such a case we do not have to give value for parameters,

the program will use the default ones.  Unfortunately sometimes this

is not enough. If we do not want to give values for all the

parameters, only for some of them we come across problems, because an

arbitrary set of parameters cannot be omitted. On the other hand

parameters have a fixed order in the head of the function.  C++ can

apply the default values only in the back of the order, if we do not

give other value for them.  So we can not give the function for

example the value of the first, and the third parameter, expecting

that the program will aplly the default value for the second

parameter.  However sometimes we would like to use some functinos

exactly in this way. With a crafty trick and with some little

inconvenience this is possible. We have implemented this little trick

as an example below.

\code

class named_fn 

{

  int _id;

  double _val;

  int _dim;

  public:

  named_fn() : _id(0), _val(1), _dim(2) {}

  named_fn& id(int p)     { _id  = p ; return *this; }

  named_fn& val(double p) { _val = p ; return *this; }

  named_fn& dim(int p)    { _dim = p ; return *this; }

  run() {

    printf("Here is the function itself.");

  }

};

\endcode

The usage is the following.

We have to define a class, let's call it named_fn.  Let us assume that

we would like to use a parameter, called X. In the named_fn class we

have to define an _X attribute, and an X function. The function

expects a parameter with the type of _X, and sets the value of

_X. After setting the value the function returns the class itself. The

class also have to have a function, called for example run(), we have

to implement here the original function itself. The constructor of the

class have to give all the attributes like _X the default values of

them.

If we instantiate this class, the default values will be set for the

attributes (originally the parameters), initially. If we call the X

function, we get a class with the modified parameter value of

X. Therefore we can modify any parameter-value, independent from the

order. To run the algorithm we have to call the run() function at the

end of the row.

Example: named_fn().id(3).val(2).run();

\section traits-classes Traits Classes

The procedure above can also be applied when defining classes. In this

case the type of the attributes can be changed.  Initially we have to

define a class with the default attribute types. This is the so called

Traits Class. Later on the types of these attributes can be changed,

as described below. In our software \ref lemon::DijkstraDefaultTraits is an

example of how a traits class looks like.

\section named-templ-param Named Class Template Parameters

If we would like to change the type of an attribute in a class that

was instantiated by using a traits class as a template parameter, and

the class contains named parameters, we do not have to reinstantiate

the class with new traits class. Instead of that, adaptor classes can

be used like in the following cases.

\code

Dijkstra<>::SetPredNodeMap<NullMap<Node,Node> >

\endcode

It can also be used in conjunction with other named template

parameters in arbitrary order.

\code

Dijkstra<>::SetDistMap<MyMap>::SetPredMap<NullMap<Node,Edge> >

\endcode

The result will be an instantiated Dijkstra class, in which the

DistMap and the PredMap is modified.

\section named-templ-func-param Named "Function" Template Parameters

If the class has so called wizard functions, the new class with the

modified tpye of attributes can be returned by the appropriate wizard

function. The usage of these wizard functions is the following:

*/