What can _not_ be marked pure?

[ag0aep6g via Digitalmars-d-learn]

On 09.03.2016 10:56, Guillaume Piolat wrote:
> If I understand purity correctly
> (http://klickverbot.at/blog/2012/05/purity-in-d/), every function out
> there can be marked pure as long as it doesn't modify globals, shared
> variables or do I/O?

Pure functions also can't *read* mutable globals. But then that's it, I 
think.