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#[cfg(feature = "std")]
use std::collections::{btree_map, hash_map};
/// Extends map entries with `or_try_insert_with` and `or_try_insert_with_key`.
pub trait EntryInsertExt<'a, K, V> {
/// If empty, computes the value from the default function. If the function
/// returns `Ok`, inserts the value. If `f` returns `Err`, returns the
/// error. If there is no error, returns a mutable reference to the value in
/// the entry.
///
/// # Examples
///
/// ```
/// use std::collections::HashMap;
///
/// use try_insert_ext::EntryInsertExt;
///
/// let mut map: HashMap<&str, String> = HashMap::new();
/// let s = "hoho".to_string();
///
/// let e: Result<&mut String, ()> = map
/// .entry("poneyland")
/// .or_try_insert_with(|| Err(()));
/// assert!(e.is_err());
/// map.entry("poneyland").or_try_insert_with::<_, ()>(|| Ok(s));
///
/// assert_eq!(map["poneyland"], "hoho".to_string());
/// ```
fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>(self, default: F)
-> Result<&'a mut V, E>;
/// If empty, computes the value from the default function. If the function
/// returns `Ok`, inserts the value. If `f` returns `Err`, returns the
/// error. If there is no error, returns a mutable reference to the value in
/// the entry. This method allows for generating key-derived values for
/// insertion by providing the default function a reference to the key
/// that was moved during the `.entry(key)` method call.
///
/// # Examples
///
/// ```
/// use std::collections::HashMap;
///
/// use try_insert_ext::EntryInsertExt;
///
/// let mut map: HashMap<&str, usize> = HashMap::new();
///
/// let e: Result<&mut usize, ()> = map
/// .entry("poneyland")
/// .or_try_insert_with_key(|_| Err(()));
/// assert!(e.is_err());
/// map
/// .entry("poneyland")
/// .or_try_insert_with_key::<_, ()>(|key| Ok(key.chars().count()));
///
/// assert_eq!(map["poneyland"], 9);
/// ```
fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>(
self,
default: F,
) -> Result<&'a mut V, E>;
}
#[cfg(feature = "std")]
impl<'a, K, V> EntryInsertExt<'a, K, V> for btree_map::Entry<'a, K, V>
where
K: Ord,
{
#[inline]
fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>(
self,
default: F,
) -> Result<&'a mut V, E> {
match self {
Self::Occupied(entry) => Ok(entry.into_mut()),
Self::Vacant(entry) => default().map(|default| entry.insert(default)),
}
}
#[inline]
fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>(
self,
default: F,
) -> Result<&'a mut V, E> {
match self {
Self::Occupied(entry) => Ok(entry.into_mut()),
Self::Vacant(entry) => default(entry.key()).map(|default| entry.insert(default)),
}
}
}
#[cfg(feature = "std")]
impl<'a, K, V> EntryInsertExt<'a, K, V> for hash_map::Entry<'a, K, V> {
#[inline]
fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>(
self,
default: F,
) -> Result<&'a mut V, E> {
match self {
Self::Occupied(entry) => Ok(entry.into_mut()),
Self::Vacant(entry) => default().map(|default| entry.insert(default)),
}
}
#[inline]
fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>(
self,
default: F,
) -> Result<&'a mut V, E> {
match self {
Self::Occupied(entry) => Ok(entry.into_mut()),
Self::Vacant(entry) => default(entry.key()).map(|default| entry.insert(default)),
}
}
}
#[cfg(test)]
mod tests {
#[cfg(feature = "std")]
mod btree_map {
use std::collections::BTreeMap;
use crate::EntryInsertExt;
#[test]
fn it_works_when_occupied() {
let mut map = BTreeMap::new();
map.insert(0, 0);
*map.entry(0).or_try_insert_with::<_, ()>(|| Ok(3)).unwrap() += 1;
*map.entry(0).or_try_insert_with(|| Err(())).unwrap() += 1;
assert_eq!(map.get(&0), Some(&2));
}
#[test]
fn it_works_when_vacant() {
let mut map = BTreeMap::new();
map.entry(0).or_try_insert_with::<_, ()>(|| Ok(1)).unwrap();
assert_eq!(map.get(&0), Some(&1));
}
#[test]
fn it_errors() {
let mut map = BTreeMap::<i32, i32>::new();
assert_eq!(map.entry(0).or_try_insert_with(|| Err(())), Err(()));
}
}
#[cfg(feature = "std")]
mod hash_map {
use std::collections::HashMap;
use crate::EntryInsertExt;
#[test]
fn it_works_when_occupied() {
let mut map = HashMap::new();
map.insert(0, 0);
*map.entry(0).or_try_insert_with::<_, ()>(|| Ok(3)).unwrap() += 1;
*map.entry(0).or_try_insert_with(|| Err(())).unwrap() += 1;
assert_eq!(map.get(&0), Some(&2));
}
#[test]
fn it_works_when_vacant() {
let mut map = HashMap::new();
map.entry(0).or_try_insert_with::<_, ()>(|| Ok(1)).unwrap();
assert_eq!(map.get(&0), Some(&1));
}
#[test]
fn it_errors() {
let mut map = HashMap::<i32, i32>::new();
assert_eq!(map.entry(0).or_try_insert_with(|| Err(())), Err(()));
}
}
}