# Struct arduboy_rust::heapless::IndexMap

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    pub struct IndexMap<K, V, S, const N: usize> { /* private fields */ }

Expand description

Fixed capacity `IndexMap`

Note that you cannot use `IndexMap` directly, since it is generic around the hashing algorithm in use. Pick a concrete instantiation like `FnvIndexMap` instead or create your own.

Note that the capacity of the `IndexMap` must be a power of 2.

## Examples

Since `IndexMap` cannot be used directly, we’re using its `FnvIndexMap` instantiation for this example.

    use heapless::FnvIndexMap;

    // A hash map with a capacity of 16 key-value pairs allocated on the stack
    let mut book_reviews = FnvIndexMap::<_, _, 16>::new();

    // review some books.
    book_reviews.insert("Adventures of Huckleberry Finn",    "My favorite book.").unwrap();
    book_reviews.insert("Grimms' Fairy Tales",               "Masterpiece.").unwrap();
    book_reviews.insert("Pride and Prejudice",               "Very enjoyable.").unwrap();
    book_reviews.insert("The Adventures of Sherlock Holmes", "Eye lyked it alot.").unwrap();

    // check for a specific one.
    if !book_reviews.contains_key("Les Misérables") {
        println!("We've got {} reviews, but Les Misérables ain't one.",
                 book_reviews.len());
    }

    // oops, this review has a lot of spelling mistakes, let's delete it.
    book_reviews.remove("The Adventures of Sherlock Holmes");

    // look up the values associated with some keys.
    let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
    for book in &to_find {
        match book_reviews.get(book) {
            Some(review) => println!("{}: {}", book, review),
            None => println!("{} is unreviewed.", book)
        }
    }

    // iterate over everything.
    for (book, review) in &book_reviews {
        println!("{}: \"{}\"", book, review);
    }

## Implementations§

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### impl<K, V, S, const N: usize> IndexMap<K, V, BuildHasherDefault<S>, N>

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#### pub const fn new() -> IndexMap<K, V, BuildHasherDefault<S>, N>

Creates an empty `IndexMap`.

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### impl<K, V, S, const N: usize> IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher,

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#### pub fn capacity(&self) -> usize

Returns the number of elements the map can hold

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#### pub fn keys(&self) -> impl Iterator<Item = &K>

Return an iterator over the keys of the map, in their order

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert("a", 1).unwrap();
    map.insert("b", 2).unwrap();
    map.insert("c", 3).unwrap();

    for key in map.keys() {
        println!("{}", key);
    }

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#### pub fn values(&self) -> impl Iterator<Item = &V>

Return an iterator over the values of the map, in their order

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert("a", 1).unwrap();
    map.insert("b", 2).unwrap();
    map.insert("c", 3).unwrap();

    for val in map.values() {
        println!("{}", val);
    }

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#### pub fn values_mut(&mut self) -> impl Iterator<Item = &mut V>

Return an iterator over mutable references to the the values of the map, in their order

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert("a", 1).unwrap();
    map.insert("b", 2).unwrap();
    map.insert("c", 3).unwrap();

    for val in map.values_mut() {
        *val += 10;
    }

    for val in map.values() {
        println!("{}", val);
    }

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#### pub fn iter(&self) -> Iter<'_, K, V>

Return an iterator over the key-value pairs of the map, in their order

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert("a", 1).unwrap();
    map.insert("b", 2).unwrap();
    map.insert("c", 3).unwrap();

    for (key, val) in map.iter() {
        println!("key: {} val: {}", key, val);
    }

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#### pub fn iter_mut(&mut self) -> IterMut<'_, K, V>

Return an iterator over the key-value pairs of the map, in their order

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert("a", 1).unwrap();
    map.insert("b", 2).unwrap();
    map.insert("c", 3).unwrap();

    for (_, val) in map.iter_mut() {
        *val = 2;
    }

    for (key, val) in &map {
        println!("key: {} val: {}", key, val);
    }

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#### pub fn first(&self) -> Option<(&K, &V)>

Get the first key-value pair

Computes in O(1) time

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#### pub fn first_mut(&mut self) -> Option<(&K, &mut V)>

Get the first key-value pair, with mutable access to the value

Computes in O(1) time

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#### pub fn last(&self) -> Option<(&K, &V)>

Get the last key-value pair

Computes in O(1) time

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#### pub fn last_mut(&mut self) -> Option<(&K, &mut V)>

Get the last key-value pair, with mutable access to the value

Computes in O(1) time

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

Returns an entry for the corresponding key

    use heapless::FnvIndexMap;
    use heapless::Entry;
    let mut map = FnvIndexMap::<_, _, 16>::new();
    if let Entry::Vacant(v) = map.entry("a") {
        v.insert(1).unwrap();
    }
    if let Entry::Occupied(mut o) = map.entry("a") {
        println!("found {}", *o.get()); // Prints 1
        o.insert(2);
    }
    // Prints 2
    println!("val: {}", *map.get("a").unwrap());

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#### pub fn len(&self) -> usize

Return the number of key-value pairs in the map.

Computes in O(1) time.

    use heapless::FnvIndexMap;

    let mut a = FnvIndexMap::<_, _, 16>::new();
    assert_eq!(a.len(), 0);
    a.insert(1, "a").unwrap();
    assert_eq!(a.len(), 1);

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#### pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Computes in O(1) time.

    use heapless::FnvIndexMap;

    let mut a = FnvIndexMap::<_, _, 16>::new();
    assert!(a.is_empty());
    a.insert(1, "a");
    assert!(!a.is_empty());

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#### pub fn clear(&mut self)

Remove all key-value pairs in the map, while preserving its capacity.

Computes in O(n) time.

    use heapless::FnvIndexMap;

    let mut a = FnvIndexMap::<_, _, 16>::new();
    a.insert(1, "a");
    a.clear();
    assert!(a.is_empty());

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#### pub fn get<Q>(&self, key: &Q) -> Option<&V>where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a reference to the value corresponding to the key.

The key may be any borrowed form of the map’s key type, but `Hash` and `Eq` on the borrowed form must match those for the key type.

Computes in O(1) time (average).

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 16>::new();
    map.insert(1, "a").unwrap();
    assert_eq!(map.get(&1), Some(&"a"));
    assert_eq!(map.get(&2), None);

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#### pub fn contains_key<Q>(&self, key: &Q) -> boolwhere K: Borrow<Q>, Q: Eq + Hash + ?Sized,

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

The key may be any borrowed form of the map’s key type, but `Hash` and `Eq` on the borrowed form must match those for the key type.

Computes in O(1) time (average).

##### Examples

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 8>::new();
    map.insert(1, "a").unwrap();
    assert_eq!(map.contains_key(&1), true);
    assert_eq!(map.contains_key(&2), false);

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#### pub fn get_mut<Q, 'v>(&'v mut self, key: &Q) -> Option<&'v mut V>where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Returns a mutable reference to the value corresponding to the key.

The key may be any borrowed form of the map’s key type, but `Hash` and `Eq` on the borrowed form must match those for the key type.

Computes in O(1) time (average).

##### Examples

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 8>::new();
    map.insert(1, "a").unwrap();
    if let Some(x) = map.get_mut(&1) {
        *x = "b";
    }
    assert_eq!(map[&1], "b");

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#### pub fn insert(&mut self, key: K, value: V) -> Result<Option<V>, (K, V)>

Inserts a key-value pair into the map.

If an equivalent key already exists in the map: the key remains and retains in its place in the order, its corresponding value is updated with `value` and the older value is returned inside `Some(_)`.

If no equivalent key existed in the map: the new key-value pair is inserted, last in order, and `None` is returned.

Computes in O(1) time (average).

See also entry if you you want to insert or modify or if you need to get the index of the corresponding key-value pair.

##### Examples

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 8>::new();
    assert_eq!(map.insert(37, "a"), Ok(None));
    assert_eq!(map.is_empty(), false);

    map.insert(37, "b");
    assert_eq!(map.insert(37, "c"), Ok(Some("b")));
    assert_eq!(map[&37], "c");

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

Same as `swap_remove`

Computes in O(1) time (average).

##### Examples

    use heapless::FnvIndexMap;

    let mut map = FnvIndexMap::<_, _, 8>::new();
    map.insert(1, "a").unwrap();
    assert_eq!(map.remove(&1), Some("a"));
    assert_eq!(map.remove(&1), None);

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#### pub fn swap_remove<Q>(&mut self, key: &Q) -> Option<V>where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Remove the key-value pair equivalent to `key` and return its value.

Like `Vec::swap_remove`, the pair is removed by swapping it with the last element of the map and popping it off. This perturbs the postion of what used to be the last element!

Return `None` if `key` is not in map.

Computes in O(1) time (average).

## Trait Implementations§

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### impl<K, V, S, const N: usize> Clone for IndexMap<K, V, S, N>where K: Eq + Hash + Clone, V: Clone, S: Clone,

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#### fn clone(&self) -> IndexMap<K, V, S, N>

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl<K, V, S, const N: usize> Debug for IndexMap<K, V, S, N>where K: Eq + Hash + Debug, V: Debug, S: BuildHasher,

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

Formats the value using the given formatter. Read more
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### impl<K, V, S, const N: usize> Default for IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher + Default,

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#### fn default() -> IndexMap<K, V, S, N>

Returns the “default value” for a type. Read more
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### impl<'a, K, V, S, const N: usize> Extend<(&'a K, &'a V)> for IndexMap<K, V, S, N>where K: Eq + Hash + Copy, V: Copy, S: BuildHasher,

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#### fn extend<I>(&mut self, iterable: I)where I: IntoIterator<Item = (&'a K, &'a V)>,

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one`)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one`)
Reserves capacity in a collection for the given number of additional elements. Read more
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### impl<K, V, S, const N: usize> Extend<(K, V)> for IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher,

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#### fn extend<I>(&mut self, iterable: I)where I: IntoIterator<Item = (K, V)>,

Extends a collection with the contents of an iterator. Read more
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#### fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (`extend_one`)
Extends a collection with exactly one element.
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#### fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (`extend_one`)
Reserves capacity in a collection for the given number of additional elements. Read more
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### impl<K, V, S, const N: usize> FromIterator<(K, V)> for IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher + Default,

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#### fn from_iter<I>(iterable: I) -> IndexMap<K, V, S, N>where I: IntoIterator<Item = (K, V)>,

Creates a value from an iterator. Read more
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### impl<'a, K, Q, V, S, const N: usize> Index<&'a Q> for IndexMap<K, V, S, N>where K: Eq + Hash + Borrow<Q>, Q: Eq + Hash + ?Sized, S: BuildHasher,

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#### type Output = V

The returned type after indexing.
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#### fn index(&self, key: &Q) -> &V

Performs the indexing (`container[index]`) operation. Read more
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### impl<'a, K, Q, V, S, const N: usize> IndexMut<&'a Q> for IndexMap<K, V, S, N>where K: Eq + Hash + Borrow<Q>, Q: Eq + Hash + ?Sized, S: BuildHasher,

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#### fn index_mut(&mut self, key: &Q) -> &mut V

Performs the mutable indexing (`container[index]`) operation. Read more
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### impl<'a, K, V, S, const N: usize> IntoIterator for &'a IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher,

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#### type Item = (&'a K, &'a V)

The type of the elements being iterated over.
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#### type IntoIter = Iter<'a, K, V>

Which kind of iterator are we turning this into?
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#### fn into_iter(self) -> <&'a IndexMap<K, V, S, N> as IntoIterator>::IntoIter

Creates an iterator from a value. Read more
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### impl<'a, K, V, S, const N: usize> IntoIterator for &'a mut IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher,

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#### type Item = (&'a K, &'a mut V)

The type of the elements being iterated over.
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#### type IntoIter = IterMut<'a, K, V>

Which kind of iterator are we turning this into?
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#### fn into_iter(self) -> <&'a mut IndexMap<K, V, S, N> as IntoIterator>::IntoIter

Creates an iterator from a value. Read more
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### impl<K, V, S, const N: usize> IntoIterator for IndexMap<K, V, S, N>where K: Eq + Hash, S: BuildHasher,

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#### type Item = (K, V)

The type of the elements being iterated over.
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#### type IntoIter = IntoIter<K, V, N>

Which kind of iterator are we turning this into?
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#### fn into_iter(self) -> <IndexMap<K, V, S, N> as IntoIterator>::IntoIter

Creates an iterator from a value. Read more
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### impl<K, V, S, S2, const N: usize, const N2: usize> PartialEq<IndexMap<K, V, S2, N2>> for IndexMap<K, V, S, N>where K: Eq + Hash, V: Eq, S: BuildHasher, S2: BuildHasher,

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#### fn eq(&self, other: &IndexMap<K, V, S2, N2>) -> bool

This method tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl<K, V, S, const N: usize> Eq for IndexMap<K, V, S, N>where K: Eq + Hash, V: Eq, S: BuildHasher,

## Auto Trait Implementations§

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### impl<K, V, S, const N: usize> RefUnwindSafe for IndexMap<K, V, S, N>where K: RefUnwindSafe, S: RefUnwindSafe, V: RefUnwindSafe,

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### impl<K, V, S, const N: usize> Send for IndexMap<K, V, S, N>where K: Send, S: Send, V: Send,

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### impl<K, V, S, const N: usize> Sync for IndexMap<K, V, S, N>where K: Sync, S: Sync, V: Sync,

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### impl<K, V, S, const N: usize> Unpin for IndexMap<K, V, S, N>where K: Unpin, S: Unpin, V: Unpin,

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### impl<K, V, S, const N: usize> UnwindSafe for IndexMap<K, V, S, N>where K: UnwindSafe, S: UnwindSafe, V: UnwindSafe,

## Blanket Implementations§

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

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for Twhere U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

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

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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.