Struct scc::hash_map::Reserve

source · 
pub struct Reserve<'h, K, V, H = RandomState>
where
    K: Eq + Hash,
    H: BuildHasher,
{ /* private fields */ }
Expand description

Reserve keeps the capacity of the associated HashMap higher than a certain level.

The HashMap does not shrink the capacity below the reserved capacity.

Implementations§

source§

impl<'h, K, V, H> Reserve<'h, K, V, H>
where K: Eq + Hash, H: BuildHasher,

source

pub fn additional_capacity(&self) -> usize

Returns the number of reserved slots.

Methods from Deref<Target = HashMap<K, V, H>>§

source

pub fn reserve( &self, additional_capacity: usize, ) -> Option<Reserve<'_, K, V, H>>

Temporarily increases the minimum capacity of the HashMap.

A Reserve is returned if the HashMap could increase the minimum capacity while the increased capacity is not exclusively owned by the returned Reserve, allowing others to benefit from it. The memory for the additional space may not be immediately allocated if the HashMap is empty or currently being resized, however once the memory is reserved eventually, the capacity will not shrink below the additional capacity until the returned Reserve is dropped.

§Errors

Returns None if a too large number is given.

§Examples
use scc::HashMap;

let hashmap: HashMap<usize, usize> = HashMap::with_capacity(1000);
assert_eq!(hashmap.capacity(), 1024);

let reserved = hashmap.reserve(10000);
assert!(reserved.is_some());
assert_eq!(hashmap.capacity(), 16384);

assert!(hashmap.reserve(usize::MAX).is_none());
assert_eq!(hashmap.capacity(), 16384);

for i in 0..16 {
    assert!(hashmap.insert(i, i).is_ok());
}
drop(reserved);

assert_eq!(hashmap.capacity(), 1024);
source

pub fn entry(&self, key: K) -> Entry<'_, K, V, H>

Gets the entry associated with the given key in the map for in-place manipulation.

§Examples
use scc::HashMap;

let hashmap: HashMap<char, u32> = HashMap::default();

for ch in "a short treatise on fungi".chars() {
    hashmap.entry(ch).and_modify(|counter| *counter += 1).or_insert(1);
}

assert_eq!(hashmap.read(&'s', |_, v| *v), Some(2));
assert_eq!(hashmap.read(&'t', |_, v| *v), Some(3));
assert!(hashmap.read(&'y', |_, v| *v).is_none());
source

pub async fn entry_async(&self, key: K) -> Entry<'_, K, V, H>

Gets the entry associated with the given key in the map for in-place manipulation.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<char, u32> = HashMap::default();

let future_entry = hashmap.entry_async('b');
source

pub fn first_entry(&self) -> Option<OccupiedEntry<'_, K, V, H>>

Gets the first occupied entry for in-place manipulation.

The returned OccupiedEntry in combination with OccupiedEntry::next or OccupiedEntry::next_async can act as a mutable iterator over entries.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());

let mut first_entry = hashmap.first_entry().unwrap();
*first_entry.get_mut() = 2;

assert!(first_entry.next().is_none());
assert_eq!(hashmap.read(&1, |_, v| *v), Some(2));
source

pub async fn first_entry_async(&self) -> Option<OccupiedEntry<'_, K, V, H>>

Gets the first occupied entry for in-place manipulation.

The returned OccupiedEntry in combination with OccupiedEntry::next or OccupiedEntry::next_async can act as a mutable iterator over entries.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<char, u32> = HashMap::default();

let future_entry = hashmap.first_entry_async();
source

pub fn any_entry<P: FnMut(&K, &V) -> bool>( &self, pred: P, ) -> Option<OccupiedEntry<'_, K, V, H>>

Finds any entry satisfying the supplied predicate for in-place manipulation.

The returned OccupiedEntry in combination with OccupiedEntry::next or OccupiedEntry::next_async can act as a mutable iterator over entries.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.insert(2, 3).is_ok());

let mut entry = hashmap.any_entry(|k, _| *k == 2).unwrap();
assert_eq!(*entry.get(), 3);
source

pub async fn any_entry_async<P: FnMut(&K, &V) -> bool>( &self, pred: P, ) -> Option<OccupiedEntry<'_, K, V, H>>

Finds any entry satisfying the supplied predicate for in-place manipulation.

The returned OccupiedEntry in combination with OccupiedEntry::next or OccupiedEntry::next_async can act as a mutable iterator over entries.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_entry = hashmap.any_entry_async(|k, _| *k == 2);
source

pub fn insert(&self, key: K, val: V) -> Result<(), (K, V)>

Inserts a key-value pair into the HashMap.

§Errors

Returns an error along with the supplied key-value pair if the key exists.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert_eq!(hashmap.insert(1, 1).unwrap_err(), (1, 1));
source

pub async fn insert_async(&self, key: K, val: V) -> Result<(), (K, V)>

Inserts a key-value pair into the HashMap.

It is an asynchronous method returning an impl Future for the caller to await.

§Errors

Returns an error along with the supplied key-value pair if the key exists.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_insert = hashmap.insert_async(11, 17);
source

pub fn upsert(&self, key: K, val: V) -> Option<V>

Upserts a key-value pair into the HashMap.

Returns the old value if the HashMap has this key present, or returns None.

§Errors

Returns an error along with the supplied key-value pair if the key exists.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.upsert(1, 0).is_none());
assert_eq!(hashmap.upsert(1, 1).unwrap(), 0);
assert_eq!(hashmap.read(&1, |_, v| *v).unwrap(), 1);
source

pub async fn upsert_async(&self, key: K, val: V) -> Option<V>

Upserts a key-value pair into the HashMap.

Returns the old value if the HashMap has this key present, or returns None. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_upsert = hashmap.upsert_async(11, 17);
source

pub fn update<Q, U, R>(&self, key: &Q, updater: U) -> Option<R>
where Q: Equivalent<K> + Hash + ?Sized, U: FnOnce(&K, &mut V) -> R,

Updates an existing key-value pair in-place.

Returns None if the key does not exist.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.update(&1, |_, _| true).is_none());
assert!(hashmap.insert(1, 0).is_ok());
assert_eq!(hashmap.update(&1, |_, v| { *v = 2; *v }).unwrap(), 2);
assert_eq!(hashmap.read(&1, |_, v| *v).unwrap(), 2);
source

pub async fn update_async<Q, U, R>(&self, key: &Q, updater: U) -> Option<R>
where Q: Equivalent<K> + Hash + ?Sized, U: FnOnce(&K, &mut V) -> R,

Updates an existing key-value pair in-place.

Returns None if the key does not exist. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
let future_update = hashmap.update_async(&1, |_, v| { *v = 2; *v });
source

pub fn remove<Q>(&self, key: &Q) -> Option<(K, V)>
where Q: Equivalent<K> + Hash + ?Sized,

Removes a key-value pair if the key exists.

Returns None if the key does not exist.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.remove(&1).is_none());
assert!(hashmap.insert(1, 0).is_ok());
assert_eq!(hashmap.remove(&1).unwrap(), (1, 0));
source

pub async fn remove_async<Q>(&self, key: &Q) -> Option<(K, V)>
where Q: Equivalent<K> + Hash + ?Sized,

Removes a key-value pair if the key exists.

Returns None if the key does not exist. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_insert = hashmap.insert_async(11, 17);
let future_remove = hashmap.remove_async(&11);
source

pub fn remove_if<Q, F: FnOnce(&mut V) -> bool>( &self, key: &Q, condition: F, ) -> Option<(K, V)>
where Q: Equivalent<K> + Hash + ?Sized,

Removes a key-value pair if the key exists and the given condition is met.

Returns None if the key does not exist or the condition was not met.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.remove_if(&1, |v| { *v += 1; false }).is_none());
assert_eq!(hashmap.remove_if(&1, |v| *v == 1).unwrap(), (1, 1));
source

pub async fn remove_if_async<Q, F: FnOnce(&mut V) -> bool>( &self, key: &Q, condition: F, ) -> Option<(K, V)>
where Q: Equivalent<K> + Hash + ?Sized,

Removes a key-value pair if the key exists and the given condition is met.

Returns None if the key does not exist or the condition was not met. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_insert = hashmap.insert_async(11, 17);
let future_remove = hashmap.remove_if_async(&11, |_| true);
source

pub fn get<Q>(&self, key: &Q) -> Option<OccupiedEntry<'_, K, V, H>>
where Q: Equivalent<K> + Hash + ?Sized,

Gets an OccupiedEntry corresponding to the key for in-place modification.

OccupiedEntry exclusively owns the entry, preventing others from gaining access to it: use read if read-only access is sufficient.

Returns None if the key does not exist.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.get(&1).is_none());
assert!(hashmap.insert(1, 10).is_ok());
assert_eq!(*hashmap.get(&1).unwrap().get(), 10);

*hashmap.get(&1).unwrap() = 11;
assert_eq!(*hashmap.get(&1).unwrap(), 11);
source

pub async fn get_async<Q>(&self, key: &Q) -> Option<OccupiedEntry<'_, K, V, H>>
where Q: Equivalent<K> + Hash + ?Sized,

Gets an OccupiedEntry corresponding to the key for in-place modification.

OccupiedEntry exclusively owns the entry, preventing others from gaining access to it: use read_async if read-only access is sufficient.

Returns None if the key does not exist. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_insert = hashmap.insert_async(11, 17);
let future_get = hashmap.get_async(&11);
source

pub fn read<Q, R, F: FnOnce(&K, &V) -> R>( &self, key: &Q, reader: F, ) -> Option<R>
where Q: Equivalent<K> + Hash + ?Sized,

Reads a key-value pair.

Returns None if the key does not exist.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.read(&1, |_, v| *v).is_none());
assert!(hashmap.insert(1, 10).is_ok());
assert_eq!(hashmap.read(&1, |_, v| *v).unwrap(), 10);
source

pub async fn read_async<Q, R, F: FnOnce(&K, &V) -> R>( &self, key: &Q, reader: F, ) -> Option<R>
where Q: Equivalent<K> + Hash + ?Sized,

Reads a key-value pair.

Returns None if the key does not exist. It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();
let future_insert = hashmap.insert_async(11, 17);
let future_read = hashmap.read_async(&11, |_, v| *v);
source

pub fn contains<Q>(&self, key: &Q) -> bool
where Q: Equivalent<K> + Hash + ?Sized,

Returns true if the HashMap contains a value for the specified key.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(!hashmap.contains(&1));
assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.contains(&1));
source

pub async fn contains_async<Q>(&self, key: &Q) -> bool
where Q: Equivalent<K> + Hash + ?Sized,

Returns true if the HashMap contains a value for the specified key.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_contains = hashmap.contains_async(&1);
source

pub fn scan<F: FnMut(&K, &V)>(&self, scanner: F)

Scans all the entries.

Key-value pairs that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same key-value pair can be visited more than once if the HashMap gets resized by another thread.

§Examples
use scc::HashMap;

let hashmap: HashMap<usize, usize> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.insert(2, 1).is_ok());

let mut sum = 0;
hashmap.scan(|k, v| { sum += *k + *v; });
assert_eq!(sum, 4);
source

pub async fn scan_async<F: FnMut(&K, &V)>(&self, scanner: F)

Scans all the entries.

Key-value pairs that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same key-value pair can be visited more than once if the HashMap gets resized by another task.

§Examples
use scc::HashMap;

let hashmap: HashMap<usize, usize> = HashMap::default();

let future_insert = hashmap.insert_async(1, 0);
let future_scan = hashmap.scan_async(|k, v| println!("{k} {v}"));
source

pub fn any<P: FnMut(&K, &V) -> bool>(&self, pred: P) -> bool

Searches for any entry that satisfies the given predicate.

Key-value pairs that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same key-value pair can be visited more than once if the HashMap gets resized by another thread.

Returns true as soon as an entry satisfying the predicate is found.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.insert(2, 1).is_ok());
assert!(hashmap.insert(3, 2).is_ok());

assert!(hashmap.any(|k, v| *k == 1 && *v == 0));
assert!(!hashmap.any(|k, v| *k == 2 && *v == 0));
source

pub async fn any_async<P: FnMut(&K, &V) -> bool>(&self, pred: P) -> bool

Searches for any entry that satisfies the given predicate.

Key-value pairs that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same key-value pair can be visited more than once if the HashMap gets resized by another task.

It is an asynchronous method returning an impl Future for the caller to await.

Returns true as soon as an entry satisfying the predicate is found.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_insert = hashmap.insert_async(1, 0);
let future_any = hashmap.any_async(|k, _| *k == 1);
source

pub fn retain<F: FnMut(&K, &mut V) -> bool>(&self, pred: F)

Retains the entries specified by the predicate.

This method allows the predicate closure to modify the value field.

Entries that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same entry can be visited more than once if the HashMap gets resized by another thread.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert!(hashmap.insert(2, 1).is_ok());
assert!(hashmap.insert(3, 2).is_ok());

hashmap.retain(|k, v| *k == 1 && *v == 0);

assert!(hashmap.contains(&1));
assert!(!hashmap.contains(&2));
assert!(!hashmap.contains(&3));
source

pub async fn retain_async<F: FnMut(&K, &mut V) -> bool>(&self, pred: F)

Retains the entries specified by the predicate.

This method allows the predicate closure to modify the value field.

Entries that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same entry can be visited more than once if the HashMap gets resized by another thread.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_insert = hashmap.insert_async(1, 0);
let future_retain = hashmap.retain_async(|k, v| *k == 1);
source

pub fn prune<F: FnMut(&K, V) -> Option<V>>(&self, pred: F)

Prunes the entries specified by the predicate.

If the value is consumed by the predicate, in other words, if the predicate returns None, the entry is removed, otherwise the entry is retained.

Entries that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same entry can be visited more than once if the HashMap gets resized by another thread.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, String> = HashMap::default();

assert!(hashmap.insert(1, String::from("1")).is_ok());
assert!(hashmap.insert(2, String::from("2")).is_ok());
assert!(hashmap.insert(3, String::from("3")).is_ok());

hashmap.prune(|k, v| if *k == 1 { Some(v) } else { None });
assert_eq!(hashmap.len(), 1);
source

pub async fn prune_async<F: FnMut(&K, V) -> Option<V>>(&self, pred: F)

Prunes the entries specified by the predicate.

If the value is consumed by the predicate, in other words, if the predicate returns None, the entry is removed, otherwise the entry is retained.

Entries that have existed since the invocation of the method are guaranteed to be visited if they are not removed, however the same entry can be visited more than once if the HashMap gets resized by another thread.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_insert = hashmap.insert_async(1, 0);
let future_prune = hashmap.prune_async(|k, v| if *k == 1 { Some(v) } else { None });
source

pub fn clear(&self)

Clears the HashMap by removing all key-value pairs.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
hashmap.clear();

assert!(!hashmap.contains(&1));
source

pub async fn clear_async(&self)

Clears the HashMap by removing all key-value pairs.

It is an asynchronous method returning an impl Future for the caller to await.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

let future_insert = hashmap.insert_async(1, 0);
let future_clear = hashmap.clear_async();
source

pub fn len(&self) -> usize

Returns the number of entries in the HashMap.

It reads the entire metadata area of the bucket array to calculate the number of valid entries, making its time complexity O(N). Furthermore, it may overcount entries if an old bucket array has yet to be dropped.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.insert(1, 0).is_ok());
assert_eq!(hashmap.len(), 1);
source

pub fn is_empty(&self) -> bool

Returns true if the HashMap is empty.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert!(hashmap.is_empty());
assert!(hashmap.insert(1, 0).is_ok());
assert!(!hashmap.is_empty());
source

pub fn capacity(&self) -> usize

Returns the capacity of the HashMap.

§Examples
use scc::HashMap;

let hashmap_default: HashMap<u64, u32> = HashMap::default();
assert_eq!(hashmap_default.capacity(), 0);

assert!(hashmap_default.insert(1, 0).is_ok());
assert_eq!(hashmap_default.capacity(), 64);

let hashmap: HashMap<u64, u32> = HashMap::with_capacity(1000);
assert_eq!(hashmap.capacity(), 1024);
source

pub fn capacity_range(&self) -> RangeInclusive<usize>

Returns the current capacity range of the HashMap.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::default();

assert_eq!(hashmap.capacity_range(), 0..=(1_usize << (usize::BITS - 1)));

let reserved = hashmap.reserve(1000);
assert_eq!(hashmap.capacity_range(), 1000..=(1_usize << (usize::BITS - 1)));
source

pub fn bucket_index<Q>(&self, key: &Q) -> usize
where Q: Equivalent<K> + Hash + ?Sized,

Returns the index of the bucket that may contain the key.

The method returns the index of the bucket associated with the key. The number of buckets can be calculated by dividing 32 into the capacity.

§Examples
use scc::HashMap;

let hashmap: HashMap<u64, u32> = HashMap::with_capacity(1024);

let bucket_index = hashmap.bucket_index(&11);
assert!(bucket_index < hashmap.capacity() / 32);

Trait Implementations§

source§

impl<'h, K, V, H> AsRef<HashMap<K, V, H>> for Reserve<'h, K, V, H>
where K: Eq + Hash, H: BuildHasher,

source§

fn as_ref(&self) -> &HashMap<K, V, H>

Converts this type into a shared reference of the (usually inferred) input type.
source§

impl<'h, K, V, H> Debug for Reserve<'h, K, V, H>
where K: Eq + Hash, H: BuildHasher,

source§

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

impl<'h, K, V, H> Deref for Reserve<'h, K, V, H>
where K: Eq + Hash, H: BuildHasher,

§

type Target = HashMap<K, V, H>

The resulting type after dereferencing.
source§

fn deref(&self) -> &Self::Target

Dereferences the value.
source§

impl<'h, K, V, H> Drop for Reserve<'h, K, V, H>
where K: Eq + Hash, H: BuildHasher,

source§

fn drop(&mut self)

Executes the destructor for this type. Read more

Auto Trait Implementations§

§

impl<'h, K, V, H> Freeze for Reserve<'h, K, V, H>

§

impl<'h, K, V, H> RefUnwindSafe for Reserve<'h, K, V, H>
where H: RefUnwindSafe,

§

impl<'h, K, V, H> Send for Reserve<'h, K, V, H>
where H: Sync, K: Sync, V: Sync,

§

impl<'h, K, V, H> Sync for Reserve<'h, K, V, H>
where H: Sync, K: Sync, V: Sync,

§

impl<'h, K, V, H> Unpin for Reserve<'h, K, V, H>

§

impl<'h, K, V, H> UnwindSafe for Reserve<'h, K, V, H>
where H: RefUnwindSafe,

Blanket Implementations§

source§

impl<T> Any for T
where T: 'static + ?Sized,

source§

fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for T
where T: ?Sized,

source§

fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

source§

fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

impl<T> From<T> for T

source§

fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T, U> Into<U> for T
where U: From<T>,

source§

fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

source§

impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.