Impl From<Peekable> for Iterator

[Folyd]

Currently, we have no way to get back to origin Iterator after call peekable(),
this PR impl From<Peekable<I>> trait for Iterator.

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[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain)

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   Compiling compiler_builtins v0.1.138
error: implementation has missing stability attribute
  --> library/core/src/iter/adapters/peekable.rs:52:1
   |
52 | / impl<I: Iterator> From<Peekable<I>> for I {
53 | |     fn from(p: Peekable<I>) -> Self {
54 | |         p.iter
56 | | }
   | |_^

error: could not compile `core` (lib) due to 1 previous error

[Noratrieb]

Thank you for the PR! This PR contains a public library API change, which should follow the proper process of creating an ACP first: https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html
Use @rustbot ready when your ACP has been accepeted.
@rustbot author

Personally, I think having an inherent into_inner method would make more sense.

[cuviper]

There have been previous rejected ACPs for this:

• Add inner and into_inner methods to iterator adapters  libs-team#128 (comment)
• Add inner methods to some iterators libs-team#430

[Folyd]

Thanks for let me know the ACP. Is reasonable to only add From trait impl instead adding inner()/into_inner()?

[oli-obk]

I don't see this PR being accepted in its current state or with modifications. The rationale from the previous attempts still apply, so I'm closing it.

The T-libs result was to write your own iterators or to use by_ref to preserve the original iterator