How does Linq-to-Xml convert objects to strings?

Linq-to-Xml contains lots of methods that allow you to add arbitrary objects to an xml tree. These objects are converted to strings by some means, but I can't seem to find the specification of how this occurs. The conversion I'm referring to is mentioned (but not specified) in MSDN.

I happen to need this for javascript interop, but that doesn't much matter to the question.

Linq to Xml isn't just calling .ToString(). Firstly, it'll accept null elements, and secondly, it's doing things no .ToString() implementation does:

For example:

new XElement开发者_开发技巧("elem",true).ToString() == "<elem>true</elem>"
//but...
true.ToString() == "True" //IIRC, this is culture invariant, but in any case...
true.ToString(CultureInfo.InvariantCulture) == "True"

Other basic data types are similarly specially treated.

So, does anybody know what it's doing and where that's described?

Earmon, you are correct.

A quick visit with Reflector* reveals that XElement and friends will try to cast the value to all the 'simple' types, and then call an appropriate XmlConvert.ToString() method.

Here's an (slightly edited) excerpt, for illustration:

if (value is string)
{
    str = (string) value;
}
else if (value is double)
{
    str = XmlConvert.ToString((double) value);
}
// ...

If the object is not a 'simple' type, then obj.ToString() will be used.

This is very nice, because that's almost the only right way to do it.

Of course, you normally want to take with a grain of salt anything based on "that's how it is today". Indeed, MS might one day change how they do it. We don't care -- what matters is that the semantics are carved in stone.

*(Product links are always provided for convenience. I have no relationship with the product or its manufacturer, other than being an indirect customer.)

Update: In Introducing Microsoft LINQ, Pialorsi and Russo confirm this for the other side of the equation (extracting values and casting them), on page 172:

[when casting an XElement to a given type like Decimal] ...the various Explicit [cast] operator overloads internally use XmlConvert from System.Xml or Parse methods of .NET types.

Although I can't find MSDN documentation to support this, when you do something like new XElement("bla",false) the System.Xml.XmlConvert class is uses to (de-)serialize the data in a non-localized fashion.

In other words, if anyone else needs to know what exactly linq to xml does when you add a (non-xml) object into an xml tree, look at System.Xml.XmlConvert.