Chris Hartjes has a reminder posted to his blog today in the form of this recent post that "scope is not a mouthwash" - personal experience from his recent development where he forgot about something as simple as scoping (and it caused him all sorts of headaches).

For [a chapter in my book on dependency injection] I am using Pimple, an incredibly small but effective dependency injection container. Easy to use, simple and effective documentation, just what I was looking for. I also noticed that Pimple supported the use of closures (or anonymous functions) as a way of storing a dependency. Then things got stupid.

He shares a bit of code showing how he added it to his bootstrap but was given a "cannot find class" error when he tried to use the tool. He walks through the steps he followed to track down the problem - looking closer at Pimple, investigating closures and, the ultimate problem, namespace scoping. He was missing a "" to start his namespace and closures work slightly differently:

So why does it behave differently inside closures? I am not 100% sure, but if I had to make an educated guess I would say that when trying to resolve namespaces inside a closure, the interpretor doesn't assume that it is already inside the global namespace, that it is in a namespace of it's own.