PHP DateTime for .NET Developers PHP's DateTime class has the two methods add() and sub() to add or subtract a time span from a DateTime object. This looks very familiar to me, in .NET I can do the same thing. But once I tried it, it did very strange things. I found out that in PHP, those methods will modify the object itself. This is not documented and the return value type indicates otherwise. Okay, so in some scenarios I need three lines