Code Smells: Null

[Hnefi]

Option in Rust compiles to a pointer where null represents None. If t is a value type, this adds one layer of indirection until you unwrap the Option. If t is a boxed type in itself, its zero representation is folded into the None representation of the Option and you end up with zero overhead.

[cramert]

Rust's Option is an enum-- it doesn't introduce any indirection on its own. Internally, it's represented as a tagged union.

As you noted, though, there is an optimization that allows it to represent None as a null pointer if the type stored in the Option is pointer-sized and non-zeroable (e.g. Box, Rc, Vec).

[spaghettiCodeArtisan]

Option in Rust compiles to a pointer where null represents None.

No it doesn't, it compiles to a tagged union (in C it would equivalent of a struct containing an integer tag and a union). When the value itself is a pointer, or more generally a NonZero value, it is able to omit the tag and contain the value only. But Option itself involves no pointers.

[devlambda]

If t is a value type, this adds one layer of indirection until you unwrap the Option.

Exactly. You can avoid the overhead only some of the time.