Console: Documentation fixes

[senf.git] / Console / Mainpage.dox

// $Id$
//
// Copyright (C) 2008 
// Fraunhofer Institute for Open Communication Systems (FOKUS)
// Competence Center NETwork research (NET), St. Augustin, GERMANY
//     Stefan Bund <g0dil@berlios.de>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
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//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the
// Free Software Foundation, Inc.,
// 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

/** \mainpage The Configuration and Runtime Control Library

    The Console library implements a runtime interactive (network) console which allows to
    configure, control and manipulate a running application in any way. Additionally this library
    provides support for configuration files and command line parsing which can be used with or
    without the network console.

    \autotoc

    \section console_intro Introduction

    There are three parts to the Config/console library:

    \li The console/config library is based on a \link node_tree tree of console/config
        nodes. \endlink
    \li Besides directories, the node contains command nodes. Commands are based on \link
        console_commands variables or callbacks.\endlink
    \li The console/config library is utilized by writing configuration files or interactive
        commands in \link console_parser the console/config language.\endlink

    The node tree works like a directory structure. Commands are entered into this directory
    structure and can be called passing arbitrary arguments. Configuration parameters are just
    commands which set their respective parameter, however the library allows commands to do much
    more than just that.

    \section console_example Example

    The following example shows a \e very short summary on how to integrate the config/console
    library. See above links for more:

    \code
    #include <senf/Console.hh>

    // Define callback function.
    void mycommand(std::ostream & os, int foo, int bar)
    {
        // ...
        os << "!! Important message ...\n";
    }

    namespace kw = senf::console::kw;

    int main(int, char**)
    {
        // Provide global documentation
        senf::console::root()
            .doc("This is someServer server");

        // Add a command
        senf::console::root()
            .add("mycommand", &mycommand)
            .doc("If <bar> is given, flurgle the <foo>, otherwise burgle it")
            .arg("foo")
            .arg(kw::name = "bar", kw::default_value = 0);

        // Start the interactive console server
        senf::console::Server::start(senf::INet4SocketAddress(senf::INet4Address::None, 23232u))
            .name("someServer");
    }
    \endcode

    after this registration, the console can be accessed easily via telnet:
    
    <pre>
    $ telnet localhost 23232
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'
    xxxx-xx-xx xx:xx:xx.xxxxxx-0000 [NOTICE][senf::console::Server] Registered new client 0xxxxxxx
    someServer:/# ls
    mycommand
    someServer:/# mycommand
    !! Important message  ...
    someServer:/# exit
    xxxx-xx-xx xx:xx:xx.xxxxxx-0000 [NOTICE][senf::console::Server] Disposing client 0xxxxxxx
    Connection closed by foreign host.
    $
    </pre>

    \see \ref console_testserver for a complete example application

    \section intro_init Initialization

    To make the console accessible, it must be initialized when the program is started:
    \code
    #include <senf/Console.hh>

    int main(int argc, char * argv [])
    {
        // Configure console nodes, add commands ...

        // Start console server
        senf::console::start(senf::INet4SocketAddress(12345u))
           .name("myserver");

        // You need to enter the scheduler main-loop for the server to work
        senf::Scheduler::instance().process();
       
        // Alternatively enter the main-loop via the PPI
        // senf::ppi::run();
    }
    \endcode

    This will start the server on IPv4 port 12345. The servers name (as displayed in the interactive
    console prompt) is set to 'myserver'.

    After launching the application, the server can be accessed at the given port:
    \htmlonly
    <pre>
    bash$ telnet localhost 12345
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.

    myserver:/$ exit
    Connection closed by foreign host.
    bash$
    </pre>
    \endhtmlonly

    \section intro_nodes The node tree

    The basic idea is, that the console/config library manages a directory structure of parameters
    and auxiliary commands. Parameters are just commands which set a parameter value so everything
    is either a directory entry (senf::console::DirectoryNode) or a command
    (senf::console::CommandNode).
    
    \see \ref node_tree


    \section intro_commands Registering console/config commands

    The console/config language does not define, how arguments are passed to the commands, it just
    tokenizes the input and passes the tokens to the commands which then handle the
    conversion.

    Since parsing the tokens into something usable is quite tedious and error prone, the library
    implements automatic argument parsing where the argument tokens are automatically parsed
    depending on argument types. This enables you to register a command taking an integer argument
    which will be called with an already parsed integer value (or throw a
    senf::console::SyntaxErrorException if the conversion fails). This will be the most often used
    command.

    \see \ref console_commands
    

    \section intro_language The console/config language

    To call the commands and set parameters, a very simple language is defined. The language is
    almost declarative (e.g. it does not have any control-flow statements) but is processed
    imperatively from top to bottom. This is very simple and flexible.

    Commands are referenced by their path in the node tree. To simplify working with deeply nested
    directory structures, the current directory may be changed persistently or temporarily for some
    commands.
    \code
    /server/port 1234;
    
    /logger/targets/console {
        accept senf::log::Debug IMPORTANT;
        accept server::ServerLog CRITICAL;
    }
    \endcode

    \see \ref console_parser
 */

/** \defgroup console_commands Supported command types

    The Console/config library supports quite a number of different command types. All these types
    of command are registered, by passing them to DirectoryNode::add()

    \autotoc

    \section console_cmdadd Adding commands and setting attributes

    Basically, all commands are added using senf::console::DirectoryNode::add(). What exactly
    happens depends on the type of object added.
    \code
    dir.add("name", callback)
    \endcode
    will add a command 'name' which will execute 'callback' when called, where 'callback' can be a
    lot of things as documented in the following chapters.

    The add call always returns (something which can be used as) a reference to the command node
    added:
    \code
    senf::console::CommandNode & node ( dir.add( ... ) );
    \endcode

    Depending on the object added, you can also bind to a more specific node type
    (e.g. senf::console::SimpleCommand) if you know the type of node returned.

    Depending on the type of object added, there are additional attributes which can be set. These
    attributes are always set by calling them on the return value <b>before saving that value as a
    node reference</b>. It is \e not guaranteed, you can call these members on the node
    reference.
    \code
    dir.add("name", callback)
        .doc("The documentation");
    \endcode
    sets the \e doc attribute (if that is available, otherwise this will fail to compile). The
    attribute members return value is again (something which can be used as) a reference to the
    command node
    \code
    senf::console::CommandNode & node (
        dir.add("name", callback)
            .doc("The documentation") );
    \endcode


    \section console_manualparse Manually parsing command arguments

    This is the most primitive type of command. It will be called with an output stream and with a
    senf::console::ParseCommandInfo reference which holds information about the command parsed.

    From this information the command callback gets a list of arguments or tokens which then can be
    interpreted in an arbitrary way.
    \code
    void fun1(std::ostream & os, senf::console::ParseCommandInfo const & command)
    {
        // We take exactly one argument
        if (command.arguments().size() != 1) 
            raise senf::console::SyntaxErrorException("invalid number of arguments");

        senf::console::ParseCommandInfo::TokensRange & argTokens (
            command.arguments()[0]);

        // The argument must have exactly one token
        if (argTokens.size() != 1)
            raise senf::console::SyntaxErrorException("argument syntax error");

        // Retrieve the token value
        std::string arg (argTokens[0].value());

        // In this example, we just write the argument to the output stream
        os << arg << std::endl;
    }
    \endcode
    
    Registering this callback is done by simply adding it. To provide online help, pass it to
    'doc()':
    \code
    senf::console::root()
        .add("test1", &fun1)
        .doc("Usage:\n"
             "    test1 arg\n"
             "\n"
             "Echo 'arg' to the console");
    \endcode

    The callback may now be called interactively on the console by it's registered name:
    \htmlonly
    <pre>
    server:/$ test1
    invalid number of arguments
    server:/$ test1 stefan@j32.de
    stefan@j32.de
    server:/$ test1 (echo me)
    argument syntax error
    server:/$ help test1
    Usage:
        test1 arg

    Echo 'arg' to the console
    server:/$
    </pre>
    \endhtmlonly

    As you can see above, the arguments and tokens are returned as <a
    href="http://www.boost.org/doc/libs/1_33_1/libs/range/doc/utility_class.html#iter_range">
    boost::iterator_range</a> instances. These behave much like containers: They have \c begin() and
    \c end() and some other useful members.
    
    The parser will have divided the argument tokens into arguments already. This simplifies further
    parsing. If however you want to access the list of argument tokens as a single list, you can do
    so using senf::console::ParseCommandInfo::tokens().
    
    Parsing arguments is quite simple but can get very tedious. To simplify this task, the parsing
    can be delegated to the Console/config library. See the next section.

    This type of command has only a single attribute, \e doc to set the commands documentation.


    \section console_autoparse Automatic argument parsing
    
    To greatly simplify parsing complex commands, we turn to automatic argument parsing. 

    \subsection console_autoadd Adding

    Automatically parsed commands are registered by just adding a callback which has the correct
    arguments and return-value defined:
    \code
    std::string fun2(std::string const & arg)
    {
        return arg;
    }
    \endcode

    This extremely simple callback may be registered by adding it to a senf::console::DirectoryNode.
    \code
    senf::console::root()
        .add("test2", &fun2);
    \endcode
    The functionality is now identical to \c test1:
    \htmlonly
    <pre>
    server:/$ test2
    invalid number of arguments
    server:/$ test2 stefan@j32.de
    stefan@j32.de
    server:/$ test2 (echo me)
    argument syntax error
    server:/$ help test2
    Usage:
        test2 arg11:string
    server:/$
    </pre>
    \endhtmlonly


    \subsection command_ostream Accessing the console stream

    Commands may have an optional first argument of type <tt>std::ostream &</tt>. This argument is
    not considered part of the real interface. When the command is executed, the callback will be
    passed the current consoles output stream object in this argument. With this, the callback can
    output arbitrary messages to the network console.
    \code
    void fun3(std::ostream & os, unsigned n, std::string text)
    {
        while (n-- > 0) os << text << std::endl;
    }

    senf::console::root()
        .add("test3", &fun3);
    \endcode

    This simple command can now be used thus:
    \htmlonly
    <pre>
    server:/$ test3
    invalid number of arguments
    server:/$ test3 stefan@j32.de
    invalid number of arguments
    server:/$ test3 2 ok
    ok
    ok
    server:/$ help test3
    Usage:
        test3 arg11:int arg12:string
    server:/$
    </pre>
    \endhtmlonly

    \subsection command_overload Overloading

    Automatically parsed commands can be overloaded: You can register multiple commands under the
    same name. Each overload is tried in turn until no SyntaxErrorException is raised.
    \code
    senf::console::root()
        .add("test4", &fun3);
    senf::console::root()
        .add("test4", &fun2);
    \endcode
    And now, we can call \c test4 with one or two args:
    <pre>
    server:/$ test4
    invalid number of arguments
    server:/$ test4 stefan@j32.de
    stefan@j32.de
    server:/$ test4 2 ok
    ok
    ok
    server:/$ help test4
    Usage:
        1- test4 arg11:int arg12:string
        2- test4 arg21:string
    server:/$
    </pre>

    One note: When taking the address of an overloaded function (member or non-member), the C++
    language forces you to cast that address to one of the possible types so the compiler knows,
    which overload is requested. So to add a function which is overloaded in C++, each overload
    needs to be added explicitly, casting to the correct type:
    \code
    void over(int);
    void over(int,int);

    senf::console::root()
        .add("over", static_cast<void (*)(int)>(&over));
    senf::console::root()
        .add("over", static_cast<void (*)(int,int)>(&over));
    \endcode


    \subsection console_attributes Attributes

    As have seen so far, some documentation is automatically provided. We can add more info, by
    setting additional attributes. 
    \code
    senf::console::root()
        .add("test5", &fun3)
        .doc("Echo text to the console")
        .overloadDoc("Repeat {arg12} for {arg11} lines");
    senf::console::root()
        .add("test4", &fun2)
        .overloadDoc("Echo the {arg21} argument")
    \endcode

    This additional info is used to provide more documentation:
    \htmlonly
    <pre>
    server:/$ help test5
    Usage:
        1- test5 arg11:int arg12:string
        2- test5 arg21:string

    Echo text to the console

    Variant 1:
    Repeat {arg12} for {arg11} lines
    
    Variant 2:
    Echo the {arg21} argument
    senf:/$
    </pre>
    \endhtmlonly


    \subsection console_argattributes Argument attributes

    Additional attributes can be set for each parameter. They are all passed to the
    senf::console::ParsedArgumentAttributor::arg() attribute.

    \code
    namespace kw = senf::console::kw;

    senf::console::root()
        .add("test6", &fun3)
        .doc("Echo text to the console")
        .overloadDoc("Repeat {text} for {n} lines");
        .arg( kw::name = "n", kw::description="Number of repetitions" )
        .arg( kw::name = "text", kw::description="Text to output" );
    senf::console::root()
        .add("test6", &fun2)
        .overloadDoc("Echo the {text} argument")
        .arg( kw::name = "text" );
    \endcode

    (Sadly, there is no way to automatically find out the \e name of an argument, just it's type.)
    Every callback argument corresponds with a call of the \c arg() attribute. Argument attributes
    are set using keywords from the \ref senf::console::kw namespace. You will probably either use
    this namespace via a namespace alias (as above) or via a <tt>using namespace
    senf::console::kw</tt> declaration (but beware of name collisions).

    You don't need to specify any information for an argument: To skip an argument, just call \c
    arg() without attributes for this argument.

    After adding this information, the online help is much more readable
      \htmlonly
    <pre>
    server:/$ help test6
    Usage:
        1- test6 n:int text:string
        2- test6 text:string

    With:
        n         Number of repetitions
        text      Text to output

    Echo text to the console

    Variant 1:
    Repeat {text} for {n} lines
    
    Variant 2:
    Echo the {text} argument
    senf:/$
    </pre>
    \endhtmlonly

    Since most of the time, we only need to set the name and possibly a description for arguments,
    there is a shortcut: name and description can be specified as positional arguments in this
    order. So the following will give the exactly same result as above:
    \code
    namespace kw = senf::console::kw;

    senf::console::root()
        .add("test6", &fun3)
        .doc("Echo text to the console")
        .overloadDoc("Repeat <text> for <n> lines");
        .arg("n",    "Number of repetitions")
        .arg("text", "Text to output");
    senf::console::root()
        .add("test6", &fun2)
        .overloadDoc("Echo the <text> argument")
        .arg("text");
    \endcode
    
    Keyword arguments should always be used if additional attributes are set. You can however mix
    positional and keyword arguments.

    
    \subsection console_defaults Default values
    
    Another information which can not be automatically gathered from the type system is default
    values. These have to be declared explicitly:
    \code
    namespace kw = senf::console::kw;

    senf::console::root()
        .add("test7", &fun3)
        .doc("Echo {text} to the console, repeating {text} for {n} lines")
        .arg("n",    "Number of repetitions", kw::default_value=1)
        .arg("text", "Text to output");
    \endcode

    Default values can be used together with overloading. Default (optional) value support is quite
    flexible, it is not mandatory, for default values to be specified only for the trailing
    arguments. For the exact definition, how parsed argument values are assigned to overload
    arguments in the presence of default values, see \ref senf::console::kw::default_value.
    
    \htmlonly
    <pre>
    server:/$ test7 echo
    echo
    server:/$ test7 4 ok
    ok
    ok
    ok
    ok
    server:/$ help test7
    Usage:
        test4 [n:unsigned] text:string
    
    With:
        n         Number of repetitions
            default: 1
        text      Text to output

    Echo {text} to the console, repeating {text} for {n} lines
    server:/$
    </pre>
    \endhtmlonly


    \subsection console_boostfn Non-function-pointer commands

    It is possible to add other callable objects besides function (and member-function)
    pointers. However, since it is not possible to automatically deduce the argument and return
    types in this case, the callables have to be wrapped in a \c boost::function object:

    \code
    senf::console::root()
        .add("test8", 
             boost::function<void (std::ostream &, std::string const &)>(
                 boost::bind(&fun3, _1, 4u, _2)));
    \endcode

    This works with any callable object where argument types cannot be deduced automatically:
    Boost.Bind expressions, Boost.Lambda expressions, functors and so on.
    
    \htmlonly
    <pre>
    server:/$ test8 ok
    ok
    ok
    ok
    ok
    server:/$ help test8
    Usage:
        test8 arg11:string
    server:/$
    </pre>
    \endhtmlonly


    \subsection console_attr_summary Attribute summary

    Here a summary of the most common attributes

    <table class="senf fixedwidth">

    <tr><td style="width:14em">\link senf::console::ParsedArgumentAttributorBase::doc() .doc\endlink
    ( \e doc )</td><td>Set documentation for all overloads</td></tr>
    
    <tr><td>\link senf::console::ParsedArgumentAttributorBase::overloadDoc()
    .overloadDoc\endlink ( \e doc )</td><td>Set documentation for a specific overload</td></tr>

    <tr><td>\link senf::console::ParsedArgumentAttributor::arg() .arg\endlink ( \e argument \e
    attributes )</td><td>Set argument attributes (see below)</td></tr>

    </table>

    The most important argument attributes (all defined in the senf::console::kw namespace) are:
    
    <table class="senf fixed width">

    <tr><td style="width:14em">\link senf::console::kw::name kw::name\endlink</td><td>Parameter
    name</td></tr>

    <tr><td>\link senf::console::kw::description kw::description\endlink</td><td>One-line
    description of the argument</td></tr>

    <tr><td>\link senf::console::kw::default_value kw::default_value\endlink</td><td>Arguments
    default value</td></tr>

    </table>

    \see <a
        href="classsenf_1_1console_1_1ParsedArgumentAttributor-members.html">senf::console::ParsedArgumentAttributor
        / List of all members</a> for the complete attribute interface \n
        \ref senf::console::kw for a list of all argument attribute keywords

        
    \section console_memberfn Member functions
    
    Non-static member functions are supported like non-member functions (static member functions are
    identical to non-members). They must however be added through a senf::console::ScopedDirectory
    instance to bind them to their instance.
    \code
    class Test1
    {
    public:
        senf::console::ScopedDirectory<Test1> dir;

        Test1(std::string label) : dir(this), label_ (label) 
            { dir.add("test", &Test::test1);
              dir.add("test", &Test::test2); }
    
        std::string test1(std::string const & text)
            { return label_ + ": " + text; }

        void test2(std::ostream & os, unsigned n, std::string const & text) 
            { while (n-- > 0) os << label << ": " << text << std::endl; }

    private:
        std::string label_;
    };

    // ...

    Test1 test1ob ("test");
    senf::console::root().add("test1ob", test1ob.dir);
    \endcode

    Binding via senf::console::ScopedDirectory ensures, that the commands are automatically removed
    from the tree when the object is destroyed.


    \section console_variables Variables
    
    \subsection console_varadd Adding

    The console/config library supports the direct registration of variables as commands. A
    variable command consists of two overloads, one to query the current value and one to change the
    value. 
    \code
    class Test2
    {
    public:
        senf::console::ScopedDirectory<Test2> dir;

        Test2() : dir(this), var_(0)
            { dir.add("var", var_); }

    private:
        int var_;
    };

    Test2 test2ob;
    senf::console::root().add("test2ob", test2ob.dir);
    \endcode
    This shows the most common scenario: A member variable is added to a ScopedDirectory of the same
    class. This ensures, that the variable command node is removed from the tree when the instance
    (and thereby the variable) are destroyed. The variable can now be used like any other command:
    \htmlonly
    <pre>
    server:/$ test2ob/var
    0
    server:/$ test2ob/var 10
    server:/$ test2ob/var
    10
    server:/$ help test2ob
    Usage:
        1- var new_value:int
        2- var
    server:/$
    </pre>
    \endhtmlonly


    \subsection console_varro Read-only variables
    
    The library also supports read-only variables. To make a variable read-only, just wrap it in \c
    boost::cref() (where \c cref stands for \c const reference)
    \code
    int var (0);

    senf::console::root().add("var1", boost::cref(var));
    \endcode
    A read-only variable only has a single overload:
    \htmlonly
    <pre>
    server:/$ var1
    0
    server:/$ help var1
    Usage:
        var1
    server:/$ 
    </pre>
    \endhtmlonly


    \subsection console_varattr Attributes

    The most important Variable command attributes are

    <table class="senf fixedwidth">

    <tr><td style="width:14em">\link senf::console::VariableAttributor::doc() .doc\endlink
    ( \e doc )</td><td>Set variable documentation</td></tr>
    
    <tr><td>\link senf::console::VariableAttributor::onChange() .onChange\endlink
    ( \e handler )</td><td>Set change handler</td></tr>
    
    </table>

    \see senf::console::VariableAttributor for the complete attribute interface

    \subsection console_varchange Change notification

    A \e handler can be set to be called, whenever the variable is changed. It will be called with a
    reference to the old value. The handler is called, after the value has been changed

    \code
    int var (0);

    // Since this is int, it would make sense to declare the argument pass-by-value (int old)
    // but for more complex args, use a const & here
    void varChanged(int const & old)
    {
        // ...
    }

    senf::console::root().add("var2",var)
        .onChange(&varChanged);
    \endcode
    
    After this setup, \c varChanged will be called, whenever the value has changed.


    \section console_args Registering special argument types

    By default, argument types which can be read and written using \c iostreams are automatically
    supported. Other types need to be registered explicitly


    \subsection console_args_enum Registering enum types

    Enum types are a special case, since it is not possible, to find a string representation for the
    enumerator values automatically. Therefore, enum types need to be registered manually.
    \code
    enum MyEnum { Sit, Run, Jump };
    SENF_CONSOLE_REGISTER_ENUM( MyEnum, (Sit)(Run)(Jump) );

    MyEnum fun4(MyEnum v) { return v }

    senf::console::root()
        .add("test9", &fun4);
    \endcode

    After an enum type is registered, it can be used like any other type for arguments or
    return-values:

    \htmlonly
    <pre>
    server:/$ test9 Sit
    Sit
    server:/$ test9 Crawl
    argument syntax error: invalid enum value
    server:/$ help test9
    Usage:
        test9 arg11:MyEnum
    server:/$
    </pre>
    \endhtmlonly

    \ref SENF_CONSOLE_REGISTER_ENUM() can only be used, to register enums at namespace scope. To
    register enums defined within some class, use \ref SENF_CONSOLE_REGISTER_ENUM_MEMBER()

    \code
    class Test3
    {
    public:
        enum Color { Red, Green, Blue };
    
        senf::console::ScopedDirectory<MyClass> dir;

        Test3();

        Color mem3(Color c) { return c }
    };
    SENF_CONSOLE_REGISTER_ENUM_MEMBER( Test3, Color, (Red)(Green)(Blue) );

    Test3::Test3() : dir(this)
        { dir.add("test", &MyClass::mem3); }
    
    Test3 test3ob;
    senf::console::root().add("test3ob", test3ob.dir);
    \endcode

    Using this command/type is identical
    \htmlonly
    <pre>
    server:/$ test3ob/test Red
    Red
    server:/$ test3ob/test White
    argument syntax error: invalid enum value
    server:/$ help test3ob/test
    Usage:
        test arg11:Color
    </pre>
    \endhtmlonly


    \subsection console_args_custom Customizing argument and return value parsing/formatting

    To support or customize parsing/formatting of other types, they need to be registered. In it's
    simplest case, this works, by just providing an appropriate overload for
    senf_console_parse_argument() and senf_console_format_value():
    \code
    struct Coordinate
    {
        Coordinate() : x(0), y(0) {}
        Coordinate(int x_, int y_) : x(x_), y(y_) {}

        int x, y;
    }

    void senf_console_parse_argument(senf::console::ParseCommandInfo::TokensRange const & tokens,
                                     Coordinate & out)
    {
        if (tokens.size() != 2)
            throw SyntaxErrorException("parameter syntax error");
        senf::console::ArgumentTraits<int>::parse(
            senf::console::ParseCommandInfo::TokensRange( tokens.begin(), tokens.begin()+1 ),
            out.x )
        senf::console::ArgumentTraits<int>::parse(
            senf::console::ParseCommandInfo::TokensRange( tokens.begin()+1, tokens.end() ),
            out.y )
    }

    void senf_console_format_value(Coordinate const & value, std::ostream & os)
    {
        os << '(' << value.x << ' ' << value.y << ')';
    }
    \endcode
    The parser will accept an argument with two tokens which are each forwarded to the integer
    parser. The formatter writes out the value as a parenthesized pair.

    \code
    Coordinate fun5(Coordinate const & p) { return Coordinate(2*p.x, 2*p.y) }
    
    namespace kw = senf::console::kw;

    senf::console::root()
        .add("test10", &fun5)
        .arg("x","coordinate to double",
             kw::default_value = Coordinate())
    \endcode
    We can now call \c test10 with a coordinate argument:
    \htmlonly
    <pre>
    server:/$ test10 (2 7)
    (4 14)
    server:/$ help test10
    Usage:
        test10 [x:Coordinate]

    With:
        x         Coordinate to double
            default: (0 0)
    server:/$
    </pre>
    \endhtmlonly
    
    If you want to customize the formatting of default values differently from the formating of
    return-values or if you want to change the displayed name of a type, you will need to specialize
    the senf::console::ArgumentTraits class instead of implementing
    senf_console_parse_argument(). See senf::console::ArgumentTraits and
    senf::console::ReturnValueTraits for more.
 */

\f
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