carols10cents commented on issue #655:
URL: https://github.com/apache/arrow-rs/issues/655#issuecomment-899917303
So this doesn't work because specialization isn't done yet... the problem is
that if these two trait implementations:
```
impl<T: ArrowPrimitiveType, Ptr: Borrow<Option<<T as
ArrowPrimitiveType>::Native>>>
FromIterator<Ptr> for PrimitiveArray<T>
{ ... }
impl<T: ArrowPrimitiveType, Ptr: Borrow<<T as ArrowPrimitiveType>::Native>>
FromIterator<Ptr> for PrimitiveArray<T>
{ ... }
```
were allowed, then someone could come along and add:
```
impl Borrow<Option<i32>> for Integer32 { ... }
impl Borrow<i32> for Integer32 { ... }
```
and then Rust wouldn't know which `FromIterator` implementation to use.
@shepmaster helped with this answer; I only got as far as "I think it's
specialization related, but I don't know why" ;)
He also pointed me to
https://stackoverflow.com/questions/37347311/how-is-there-a-conflicting-implementation-of-from-when-using-a-generic-type,
perhaps that will be of some help to someone.
I'm working with @shepmaster on a way around this but we might not be able
to finish it until Wednesday.
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