Good Idea: safe way to transmute Vec<Option<&Foo>> to Vec<&Foo>

[Lokathor]

https://www.reddit.com/r/rust/comments/1ez6f2c/any_safe_way_to_transmute_vecoptionfoo_to_vecfoo/

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So yeah, what we want is to be able to convert from Option<&i32> to &i32, particularly within a vec/slice/container.

There's lots of types with guaranteed option representation, so we probably want to use some sort of trait.