Disallow invalid names for SceneInterface/SceneCache/IndexedIO

[johnhaddon]

This was motivated by a cache being written using "" for the name and breaking tools further down the line. We should also consider disallowing "/" in a name since we use it as a path separator. Need to consider carefully at which level of IO we do this - perhaps IndexedIO should be left alone?

[johnhaddon]

I'm just going to play devil's advocate here, and suggest an alternative approach. In a vector<InternedString> there is no ambiguity at all with any choice of name (even dumb names like "" and "/"), so why should we restrict it? The other option is to allow "/" to be escaped in the string->vector<InternedString> conversion, to disambiguate. For instance :

• /a/b/c -> [ a, b, c ]
• /a\/b/c -> [ a, /b, c ]

There's a related discussion on GafferHQ/gaffer#2070, where we're considering restricting even further to just alphanumerics. I think that's probably too much, so I'm proposing the above as an example of how we could remain totally general if we really wanted to.

[mattigruener]

Just so I have mentioned this: The solution to use just alphanumerics that I have brought up before actually wouldn't work for us because we have nodes that create objects in an array-like format:

myObjects
\ object[0]
\ object[1]