Tracking issue for Option::copied

[sugar700]

This is a tracking issue for Option::copied.

Added in #56534. Feature gate: #![feature(copied)].

Related feature: iter_copied in #57127.

[pmarcelll]

Did you mean Option::copied in the first sentence?

[sugar700]

@pmarcelll Fixed.

[alercah]

The map_clone lint in Clippy should be updated to suggest this instead when the type is copiable.

[Centril]

So we added a newtype Copied because that's what we usually do. However, in this case, we could simply reuse Cloned and implement copied as:

fn copied<'a, T>(self) -> Cloned<Self> where
    Self: Iterator<Item = &'a T>,
    T: 'a + Copy, 

Are there notable reasons not to do this that I'm missing? Doing so would substantially decrease the cost of this feature for the standard library.

[sugar700]

Cloned type wouldn't have the guarantees that Copied does, as it calls the clone method, which can have side-effects (it shouldn't, but it's not something we can depend on).

Although I suppose we currently DO expose specialization in Cloned structure when Clone implementation is incompatible with Copy implementation. This seems like a bug, so I will fix that in a separate PR.

[sugar700]

See #57970.

[SimonSapin]

The comment about the Copied type belongs in #57127. Since I see no objection to Option::copied:

@rfcbot fcp merge

[rfcbot]

Team member @SimonSapin has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Kimundi
• @SimonSapin
• @alexcrichton
• @dtolnay
• @sfackler
• @withoutboats

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