Tracking Issue for {HashMap,BTreeMap}::into_{keys,values}

[canova]

Feature gate: #![feature(map_into_keys_values)]

This is a tracking issue for {HashMap,BTreeMap}::into_{keys,values}.

Public API

// alloc::collections::btree_map

impl<K, V> BTreeMap<K, V> {
    pub fn into_keys(self) -> IntoKeys<K, V>;
    pub fn into_values(self) -> IntoValues<K, V>;
}

pub struct IntoKeys<K, V>;
pub struct IntoValues<K, V>;

impl<K, V> Iterator for IntoKeys<K, V> { type Item = K; }
impl<K, V> DoubleEndedIterator for IntoKeys<K, V> {}
impl<K, V> ExactSizeIterator for IntoKeys<K, V> {}
impl<K, V> FusedIterator for IntoKeys<K, V> {}
impl<K: Debug, V> Debug for IntoKeys<K, V> {}

impl<K, V> Iterator for IntoValues<K, V> { type Item = V; }
impl<K, V> DoubleEndedIterator for IntoValues<K, V> {}
impl<K, V> ExactSizeIterator for IntoValues<K, V> {}
impl<K, V> FusedIterator for IntoValues<K, V> {}
impl<K, V: Debug> Debug for IntoValues<K, V> {}

// alloc::collections::hash_map

impl<K: Eq + Hash, V, S: BuildHasher> HashMap<K, V, S> {
    pub fn into_keys(self) -> IntoKeys<K, V>;
    pub fn into_values(self) -> IntoValues<K, V>;
}

pub struct IntoKeys<K, V>;
pub struct IntoValues<K, V>;

impl<K, V> Iterator for IntoKeys<K, V> { type Item = K; }
impl<K, V> ExactSizeIterator for IntoKeys<K, V> {}
impl<K, V> FusedIterator for IntoKeys<K, V> {}
impl<K: Debug, V> Debug for IntoKeys<K, V> {}

impl<K, V> Iterator for IntoValues<K, V> { type Item = V; }
impl<K, V> ExactSizeIterator for IntoValues<K, V> {}
impl<K, V> FusedIterator for IntoValues<K, V> {}
impl<K, V: Debug> Debug for IntoValues<K, V> {}

Steps / History

• Requested in Add into_keys and into_values to associative maps #55214.
• Implementation: Implement into_keys and into_values for associative maps #75163
• Final commenting period (FCP)
• Stabilization PR: Stablize {HashMap,BTreeMap}::into_{keys,values} #84328

Unresolved Questions

• None yet.

[GreenBeard]

This change will be much appreciated. Could we please also have an into_entries function which returns a tuple of the key, and value?

[jplatte]

@GreenBeard that's what the into_iter methods do.

[GreenBeard]

@jplatte For some reason the documentation ( https://doc.rust-lang.org/std/collections/struct.BTreeMap.html ) has that as under "Show hidden undocumented items". Does that mean it was intentionally hidden, or is it an oversight/automatic? I didn't find it when using ctrl+f because of that.

Edit: After further reading it appears that #56073 was really what stopped me from finding it. (I assumed since the expand all kept it hidden that it was intentionally hidden by the author of the code.)

[jplatte]

@GreenBeard Right, some trait methods are hidden like that. I would generally recommend using the search built into the page rather than the browser's search for rustdoc pages. The method is easy to find if you search for BTreeMap::into_iter. But that's off-topic for this tracking issue.

[m-ou-se]

@rfcbot merge

[rfcbot]

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

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @sfackler
• @yaahc

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

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