Media independent information handling

To handle media independent data access, the GUrl base class has been implemented that represent a media in an abstract way. The class has abstract open, read, write and close method to open a media, read from it or write to it, and to close the media.

Support is implemented so far for file and string media, but in the future, direct access to ressources over the internet may become possible. A file media is implemented by the GUrlFile class, while a string media is implemented by the GUrlString class.

An example of a class making using of GUrl is the GXml class. Look at the following code:

C++

GXml xml;
xml.append(GXmlElement("dummy"));
GUrlFile   file("my_file.xml", "w");
GUrlString chain;
xml.write(file);
xml.write(chain);

Python

xml = gammalib.GXml()
xml.append(gammalib.GXmlElement('dummy'))
file  = gammalib.GUrlFile('my_file.xml', 'w')
chain = gammalib.GUrlString()
xml.write(file)
xml.write(chain)

Line 1 declares a XML object and in line 2 we append a dummy element to it. In line 3 we now create a file named my_file.xml for which we allow write access. In line 4 we allocate a string media. We then write the XML object first into the file in line 5, and then in the string in line 6. This illustrates how the GUrl classes can be used to redirect the same information to different media. Reading from different media is analoguous.