Add implementation on Option is confusing

[Kimundi]

Right now add on two Options effectively treats a None as a Some(Zero::zero()), which is:

• Unnecessary because Some(Zero::zero()) is already a valid value, why duplicate it's meaning with None?
• Contrary to the way the Maybe Monad in Haskell works: If both values are a Some, add them, else return None.

[bstrie]

I think this might be a dup of #6002, but what does this have to do with Zero::zero()?

[Kimundi]

@bstrie: Maybe I expressed it strange :)

What I mean is: If the implementation is such that Some(n) + None = Some(n), then None becomes then additive neutral element for, eg Option<uint>. But that is unnecessary because Option<uint> already has a additive neutral element: Some(0). A None is a separate value from any other Some(n), If you treat it the same as Some(0) you might as well not have an Option-value at all.

My talk about Zero::zero() was just an attempt to talk about the generic additive neutral element. :)

[Kimundi]

Anyway, this is indeed a duplicate of that issue, closing this one.