Options Sub System

## Introduction

All major SUMO applications use the same classes for parsing command line options and configuration files. These classes encapsulate parsing options from the command line and XML-configuration files and validating whether they are of a correct type. The options sub system also supports writing configuration-templates, saving current (parsed/loaded) settings to files, and printing the help screen.

## Initialising Options

### First Steps

Each application has exactly one instance of the OptionsCont (options container) - class. A reference to this class may be obtained using

    static OptionsCont &OptionsCont::getOptions();

Before an application starts registering its options, it must let OptionsCont know itself. It is needed due to the fact that OptionsCont is responsible for printing a basic information about the application and because it also generates the help screen which includes the application's name, possibly example calls, etc. Due to this, the first touch of the options sub system for each application looks similar to the following which is borrowed from netconvert_main.cpp:

       OptionsCont &oc = OptionsCont::getOptions();
       // give some application descriptions
       oc.setApplicationDescription("Road network importer / builder for the road traffic simulation SUMO.");
    #ifdef WIN32
       oc.setApplicationName("netconvert.exe", "SUMO netconvert Version " + (string)VERSION_STRING);
    #else
       oc.setApplicationName("sumo-netconvert", "SUMO netconvert Version " + (string)VERSION_STRING);
    #endif

The ifdef-block is used to differ between the supported OSes (Windows/Linux) where the SUMO-applications are named slightly different.

Please note that the description set by setApplicationDescription is a brief description and should fit into one line (be not longer than 80 characters).

### Registering Options

Before the command line options are parsed, their names, allowed types and their default values (if existing) must be inserted into this container. This mostly done within a dedicated method or function.

To insert an application option into the container, use one of the following polymorphs:

    void doRegister(const std::string &name1, Option *v);

or

    void doRegister(const std::string &name1, char abbr, Option *v);

The parameter "name1" is the name (or one of the possible names, better to say) of the inserted option. The character "abbr" within the second call is the possible one-char abbreviation of the name.

    Caution: The behavior after adding the same abbreviation for two different options is not defined.

The third parameter is an option that shall be assigned to the name(s). Remark that the OptionsCont takes the responsibility for this option - it will be deleted when the OptionsCont is deleted. The option itself must be an instance of one of the following classes, which all are derived from the class Option:

- Option_Integer
- Option_Bool
- Option_Float
- Option_String
- Option_FileName
- Option_IntVector
- Option_StringVector

The names of the classes reflect the types which are awaited as parameter for the option. Do also remark, that later access for reading should be done in dependence to the type - it means that you should not try to get a string from an Option_Float. This results in an exception.

Caution

All subclasses of Option are stored within the files ''<SUMO_HOME>/src/utils/options/Option.h and ''<SUMO_HOME>/src/utils/options/Option.cpp. This is surely not wished as when following the coding styleguide, each class should be stored in a separate pair of files. Also, one could imagine to use templates, here.

Every one of the option's subclasses has two constructors: one that is parametrised with the appropriate type and a parameter-less one. The parametrised constructor is used to supply default values for options, in the other case, no value is known to the system at first. An example: settings the "verbose"-switch as following, lets the application run quiet as default:

    oc.doRegister("verbose", 'v', new Option_Bool(false));

#### Adding Synonyms

One can also add synonyms for options. If you want to implement the option "name-of-vehicle-that-shall-halt", but you wish to have a shorter name, too, use the following to make the same option accessible using both "name-of-vehicle-that-shall-halt" and "v2h":

    oc.doRegister("name-of-vehicle-that-shall-halt", new Option_String());
    oc.addSynonyme("name-of-vehicle-that-shall-halt", "v2h");

## Retrieving Options

If no default value was supplied for an option, you should ask the OptionsCont whether it has been set. Access to values of unset options causes exceptions. This may sound hard, but as it's only the developer who accesses the options container in fact, it's the best way to assure security of the code. One can determine whether an option is set using

    bool OptionsCont::isSet(const std::string &name) const;

If one has to know whether an option still stores the default value or a value was supplied by the user, he/she may call

    bool OptionsCont::isDefault(const std::string &name) const;

Dependent on the type of an option, one can retrieve its value using the following methods from OptionsCont:

    int OptionsCont::getInt(const std::string &name) const;
    long OptionsCont::getLong(const std::string &name) const;
    std::string OptionsCont::getString(const std::string &name) const;
    float OptionsCont::getFloat(const std::string &name) const;
    const IntVector &OptionsCont::getIntVector(const std::string &name) const;
    const StringVector &OptionsCont::getStringVector(const std::string &name) const;

Using an improper method yields an exception.

You may have noticed, that there is one method to retrieve a certain value less than types available. The type Option_FileName returns a string-vector, too. The only difference is their type which allows a different processing of the values to set when parsing.

Please note, that it is good style to use the long (longest in fact) name for retrieving an option's value and that the same name (synonym) should be used at all places. This makes it easier to locate this option's usage.

## Implementation

All classes needed to store and process options can be found within <SUMO_HOME>/src/utils/options/

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