Should we really be implementing Deref and DerefMut

[tcharding]

The Rust API guidlines state that only smart pointers should implement these two traits but we are doing so. Is this correct?

links:

• https://rust-lang.github.io/api-guidelines/predictability.html#c-deref
• https://doc.rust-lang.org/book/ch15-00-smart-pointers.html

[tcharding]

If we implement Deref it implies Ordered is a smart pointer but then we are contradicting this rule:

https://rust-lang.github.io/api-guidelines/predictability.html#c-smart-ptr

[tcharding]

After more thought I believe we are right to implement Deref even though Ordered is not a smart pointer. From the docs for Deref

When to implement Deref or DerefMut
The same advice applies to both deref traits. In general, deref traits should be implemented if:

1. a value of the type transparently behaves like a value of the target type;
2. the implementation of the deref function is cheap; and
3. users of the type will not be surprised by any deref coercion behaviour.

ref: https://doc.rust-lang.org/std/ops/trait.Deref.html

To remove the contradition with C-SMART-PTR I did #25

[apoelstra]

FWIW I agree, but if/when @Kixunil comes back I'll bet he complains about this.

[Kixunil]

Aaand, now I'm going to complain! Just kidding! Actually, I think this is not abuse of Deref since it's not used to simulate OOP, it mostly obeys "a value of the type transparently behaves like a value of the target type" and there's a precedent for this in core - the ManuallyDrop type has Deref (though Drop affects program behavior much less than Ord).

[apoelstra]

there's a precedent for this in core - the ManuallyDrop type

Ooh, interesting. And yes, the OO framing of "if the outer type can be substituted for the inner type with no changes then it's ok to Deref" sounds good to me.