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 of code instead of one, plus an additional local variable. But then PHP5's copy by reference model comes into play, too. Just copying the object isn't enough, you need to explicitly clone it to not accidently modify the original instance still. So here's the C# code:

DateTime today = DateTime.Today;
...
if (date < today.Add(TimeSpan.FromDays(7)) ...

Here's the PHP equivalent:

$today = new DateTime('today');
...
$then = clone $today;
$then->add(new DateInterval('P7D'));
if ($date < $then) ...

(I keep a copy of today to have the same time for all calculations during the method runtime. I've seen it often enough that seconds or larger time units change in that time...)

Is this it in PHP? I need to write a wrapper class for that if there's no better solution! Or I'll just stay with the good ol' time() function and just use DateTime for easier parsing of the ISO date I get from the database.

$today = time() % 86400;
...
if ($date < $today + 7 * 86400) ...

Time zones not regarded in these examples.

Update: I just found out that I can use the strtotime() function as well for parsing such dates. So what's the use for a DateTime class in PHP after all if it's so complicated to use?

Update^2: I noticed that my $today = ... thing above is garbage. Well, please just imagine some correct way of getting 'today' there instead...

It looks like you will definitely have to make a clone of the object. There does not seem to be a way to create a copy of the DateTime object any other way.

As far as I can see, you could save one line:

$today = new DateTime('today');
...
$then = clone $today;
if ($then->add(new DateInterval('P7D')) < $then) ...

I agree this isn't perfect. But do stick with DateTime nevertheless - write a helper class if need be. It is way superior to the old date functions: It doesn't have the year 2038 bug, and it makes dealing with time zones much, much easiert.

http://stackoverflow.com/questions/4868709/php-datetime-for-net-developers