Trait FromIterator 

pub trait FromIterator<A>: Sized {
    // Required method
    fn from_iter<T>(iter: T) -> Self
       where T: IntoIterator<Item = A>;
}

Available on crate features crypto and std only.

Conversion from an Iterator.

By implementing FromIterator for a type, you define how it will be created from an iterator. This is common for types which describe a collection of some kind.

If you want to create a collection from the contents of an iterator, the Iterator::collect() method is preferred. However, when you need to specify the container type, FromIterator::from_iter() can be more readable than using a turbofish (e.g. ::<Vec<_>>()). See the Iterator::collect() documentation for more examples of its use.

See also: IntoIterator.

Examples

Basic usage:

let five_fives = std::iter::repeat(5).take(5);

let v = Vec::from_iter(five_fives);

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Using Iterator::collect() to implicitly use FromIterator:

let five_fives = std::iter::repeat(5).take(5);

let v: Vec<i32> = five_fives.collect();

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Using FromIterator::from_iter() as a more readable alternative to Iterator::collect():

use std::collections::VecDeque;
let first = (0..10).collect::<VecDeque<i32>>();
let second = VecDeque::from_iter(0..10);

assert_eq!(first, second);

Implementing FromIterator for your type:

// A sample collection, that's just a wrapper over Vec<T>
#[derive(Debug)]
struct MyCollection(Vec<i32>);

// Let's give it some methods so we can create one and add things
// to it.
impl MyCollection {
    fn new() -> MyCollection {
        MyCollection(Vec::new())
    }

    fn add(&mut self, elem: i32) {
        self.0.push(elem);
    }
}

// and we'll implement FromIterator
impl FromIterator<i32> for MyCollection {
    fn from_iter<I: IntoIterator<Item=i32>>(iter: I) -> Self {
        let mut c = MyCollection::new();

        for i in iter {
            c.add(i);
        }

        c
    }
}

// Now we can make a new iterator...
let iter = (0..5).into_iter();

// ... and make a MyCollection out of it
let c = MyCollection::from_iter(iter);

assert_eq!(c.0, vec![0, 1, 2, 3, 4]);

// collect works too!

let iter = (0..5).into_iter();
let c: MyCollection = iter.collect();

assert_eq!(c.0, vec![0, 1, 2, 3, 4]);

Required Methods

fn from_iter<T>(iter: T) -> Self

where T: IntoIterator<Item = A>,

Creates a value from an iterator.

See the module-level documentation for more.

Examples

let five_fives = std::iter::repeat(5).take(5);

let v = Vec::from_iter(five_fives);

assert_eq!(v, vec![5, 5, 5, 5, 5]);

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl FromIterator<()> for ()

Collapses all unit items from an iterator into one.

This is more useful when combined with higher-level abstractions, like collecting to a Result<(), E> where you only care about errors:

use std::io::*;
let data = vec![1, 2, 3, 4, 5];
let res: Result<()> = data.iter()
    .map(|x| writeln!(stdout(), "{x}"))
    .collect();
assert!(res.is_ok());

impl FromIterator<(Key, (StringValue, BaggageMetadata))> for Baggage

impl FromIterator<(String, Value)> for Map<String, Value>

impl FromIterator<Access> for Access

impl FromIterator<AsciiChar> for String

Available on non-no_global_oom_handling only.

impl FromIterator<AtFlags> for AtFlags

impl FromIterator<ByteString> for ByteString

impl FromIterator<CreateFlags> for CreateFlags

impl FromIterator<DupFlags> for DupFlags

impl FromIterator<FallocateFlags> for FallocateFlags

impl FromIterator<FdFlags> for FdFlags

impl FromIterator<IFlags> for IFlags

impl FromIterator<InterfaceFlags> for InterfaceFlags

impl FromIterator<IpAddr> for XForwardedFor

impl FromIterator<IpScopes> for IpScopes

impl FromIterator<KeyValue> for Baggage

impl FromIterator<KeyValueMetadata> for Baggage

impl FromIterator<Literal> for Seq

impl FromIterator<MemfdFlags> for MemfdFlags

impl FromIterator<Mode> for Mode

impl FromIterator<OFlags> for OFlags

impl FromIterator<OsString> for OsString

impl FromIterator<PseudoHeader> for PseudoHeaderOrder

impl FromIterator<QueryPair> for Query

impl FromIterator<ReadFlags> for ReadFlags

impl FromIterator<ReadWriteFlags> for ReadWriteFlags

impl FromIterator<RenameFlags> for RenameFlags

impl FromIterator<ResolveFlags> for ResolveFlags

impl FromIterator<SealFlags> for SealFlags

impl FromIterator<SettingId> for SettingOrder

impl FromIterator<ShutdownState> for ShutdownState

impl FromIterator<SslMode> for SslMode

impl FromIterator<SslOptions> for SslOptions

impl FromIterator<SslSessionCacheMode> for SslSessionCacheMode

impl FromIterator<SslVerifyMode> for SslVerifyMode

impl FromIterator<StatVfsMountFlags> for StatVfsMountFlags

impl FromIterator<StatxAttributes> for StatxAttributes

impl FromIterator<StatxFlags> for StatxFlags

impl FromIterator<String> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

Available on non-no_global_oom_handling only.

impl FromIterator<String> for SmolStr

impl FromIterator<String> for String

Available on non-no_global_oom_handling only.

impl FromIterator<Table> for ArrayOfTables

impl FromIterator<TokenStream> for proc_macro2::TokenStream

impl FromIterator<TokenStream> for proc_macro::TokenStream

A “flattening” operation on token streams, collects token trees from multiple token streams into a single stream.

impl FromIterator<TokenTree> for proc_macro2::TokenStream

Collects a number of token trees into a single stream.

impl FromIterator<TokenTree> for proc_macro::TokenStream

Collects a number of token trees into a single stream.

impl FromIterator<TrustAnchor<'static>> for RootCertStore

impl FromIterator<UriMatchReplaceRule> for UriMatchReplaceRuleset

impl FromIterator<UserAgentProfile> for UserAgentDatabase

impl FromIterator<ViaElement> for Via

impl FromIterator<WatchFlags> for WatchFlags

impl FromIterator<X509CheckFlags> for X509CheckFlags

impl FromIterator<X509VerifyFlags> for X509VerifyFlags

impl FromIterator<XattrFlags> for XattrFlags

impl FromIterator<char> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

Available on non-no_global_oom_handling only.

impl FromIterator<char> for ByteString

impl FromIterator<char> for SmolStr

impl FromIterator<char> for String

Available on non-no_global_oom_handling only.

impl FromIterator<u8> for ByteString

impl FromIterator<u8> for Bytes

impl FromIterator<u8> for BytesMut

impl FromIterator<u64> for StackFrames

impl FromIterator<usize> for FixedBitSet

Return a FixedBitSet containing bits set to true for every bit index in the iterator, other bits are set to false.

impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>

Available on non-no_global_oom_handling only.

impl<'a, T> FromIterator<T> for Cow<'a, [T]>

where T: Clone,

impl<'a> FromIterator<&'a AsciiChar> for String

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<&'a ByteStr> for ByteString

impl<'a> FromIterator<&'a OsStr> for OsString

impl<'a> FromIterator<&'a PseudoHeader> for PseudoHeaderOrder

impl<'a> FromIterator<&'a SettingId> for SettingOrder

impl<'a> FromIterator<&'a String> for SmolStr

impl<'a> FromIterator<&'a [u8]> for ByteString

impl<'a> FromIterator<&'a char> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<&'a char> for String

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<&'a str> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<&'a str> for ByteString

impl<'a> FromIterator<&'a str> for SmolStr

impl<'a> FromIterator<&'a str> for String

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<&'a u8> for BytesMut

impl<'a> FromIterator<AsciiChar> for Cow<'a, str>

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<AttributeTypeAndValue<'a>> for RelativeDistinguishedName<'a>

impl<'a> FromIterator<Cow<'a, OsStr>> for OsString

impl<'a> FromIterator<Cow<'a, str>> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<Cow<'a, str>> for String

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<QueryPairRef<'a>> for Query

impl<'a> FromIterator<RelativeDistinguishedName<'a>> for X509Name<'a>

impl<'a> FromIterator<String> for Cow<'a, str>

Available on non-no_global_oom_handling only.

impl<'a> FromIterator<char> for Cow<'a, str>

Available on non-no_global_oom_handling only.

impl<A, E, V> FromIterator<Result<A, E>> for Result<V, E>

where V: FromIterator<A>,

impl<A, V> FromIterator<Option<A>> for Option<V>

where V: FromIterator<A>,

impl<A> FromIterator<<A as Array>::Item> for ArrayVec<A>

where A: Array,

impl<A> FromIterator<<A as Array>::Item> for SmallVec<A>

where A: Array,

impl<A> FromIterator<<A as Array>::Item> for TinyVec<A>

where A: Array,

impl<A> FromIterator<Box<str, A>> for rama::utils::collections::smallvec::alloc::boxed::Box<str>

where A: Allocator,

Available on non-no_global_oom_handling only.

impl<A> FromIterator<Box<str, A>> for String

where A: Allocator,

Available on non-no_global_oom_handling only.

impl<F> FromIterator<F> for JoinAll<F>

where F: Future,

impl<F> FromIterator<F> for TryJoinAll<F>

where F: TryFuture,

impl<Fut> FromIterator<Fut> for FuturesOrdered<Fut>

where Fut: Future,

impl<Fut> FromIterator<Fut> for FuturesUnordered<Fut>

impl<Fut> FromIterator<Fut> for rama::futures::prelude::future::SelectAll<Fut>

where Fut: Future + Unpin,

impl<Fut> FromIterator<Fut> for SelectOk<Fut>

where Fut: TryFuture + Unpin,

impl<I> FromIterator<I> for rama::utils::collections::smallvec::alloc::boxed::Box<[I]>

Available on non-no_global_oom_handling only.

impl<I> FromIterator<I> for Box<[I]>

Available on non-no_global_oom_handling only.

impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<K, V, S> FromIterator<(K, V)> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::collections::HashMap<K, V, S>

where K: Eq + Hash, S: BuildHasher + Default,

impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>

where K: Hash + Eq, S: BuildHasher + Default,

impl<K, V, S> FromIterator<(K, V)> for LiteMap<K, V, S>

where K: Ord, S: StoreFromIterable<K, V>,

impl<K, V, S> FromIterator<(K, V)> for MultiMap<K, V, S>

where K: Eq + Hash, S: BuildHasher + Default,

impl<K, V, S> FromIterator<(K, Vec<V>)> for MultiMap<K, V, S>

where K: Eq + Hash, V: Clone, S: BuildHasher + Default,

impl<K, V> FromIterator<(K, V)> for AHashMap<K, V>

where K: Eq + Hash,

impl<K, V> FromIterator<(K, V)> for AnyValue

where K: Into<Key>, V: Into<AnyValue>,

impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V>

where K: Ord,

impl<K, V> FromIterator<(K, V)> for InlineTable

where K: Into<Key>, V: Into<Value>,

impl<K, V> FromIterator<(K, V)> for StreamMap<K, V>

where K: Hash + Eq,

impl<K, V> FromIterator<(K, V)> for Table

where K: Into<Key>, V: Into<Item>,

impl<K, V> FromIterator<(K, V)> for Trie<K, V>

where K: TrieKey,

impl<K, V> FromIterator<(K, V)> for UriParams

where K: Into<ArcStr>, V: Into<ArcStr>,

impl<K, V> FromIterator<(K, V)> for Value

where K: Into<Key>, V: Into<Value>,

impl<K, V> FromIterator<(K, V)> for serde_json::value::Value

where K: Into<String>, V: Into<Value>,

impl<P, T> FromIterator<(P, T)> for JointPrefixMap<P, T>

where P: JointPrefix,

impl<P, T> FromIterator<(P, T)> for PrefixMap<P, T>

where P: Prefix,

impl<P> FromIterator<P> for JointPrefixSet<P>

where P: JointPrefix,

impl<P> FromIterator<P> for PathBuf

where P: AsRef<Path>,

impl<P> FromIterator<P> for PrefixSet<P>

where P: Prefix,

impl<S, T> FromIterator<(S, T)> for DomainTrie<T>

where S: AsDomainRef,

impl<S> FromIterator<S> for SubdomainTrieMatcher

where S: AsDomainRef,

impl<St> FromIterator<St> for rama::futures::prelude::stream::SelectAll<St>

where St: Stream + Unpin,

impl<T, ExtendT> FromIterator<(T₁, T₂, …, Tₙ)> for (ExtendT₁, ExtendT₂, …, ExtendTₙ)

where ExtendT: Default + Extend<T>,

This implementation turns an iterator of tuples into a tuple of types which implement Default and Extend.

This is similar to Iterator::unzip, but is also composable with other FromIterator implementations:

let string = "1,2,123,4";

// Example given for a 2-tuple, but 1- through 12-tuples are supported
let (numbers, lengths): (Vec<_>, Vec<_>) = string
    .split(',')
    .map(|s| s.parse().map(|n: u32| (n, s.len())))
    .collect::<Result<_, _>>()?;

assert_eq!(numbers, [1, 2, 123, 4]);
assert_eq!(lengths, [1, 1, 3, 1]);

impl<T, F> FromIterator<F> for JoinSet<T>

where F: Future<Output = T> + Send + 'static, T: Send + 'static,

Collect an iterator of futures into a [JoinSet].

This is equivalent to calling [JoinSet::spawn] on each element of the iterator.

Examples

The main example from [JoinSet]’s documentation can also be written using collect:

use tokio::task::JoinSet;

let mut set: JoinSet<_> = (0..10).map(|i| async move { i }).collect();

let mut seen = [false; 10];
while let Some(res) = set.join_next().await {
    let idx = res.unwrap();
    seen[idx] = true;
}

for i in 0..10 {
     assert!(seen[i]);
}

impl<T, L> FromIterator<(T, L)> for Targets

where T: Into<String>, L: Into<LevelFilter>,

impl<T, P> FromIterator<Pair<T, P>> for syn::punctuated::Punctuated<T, P>

impl<T, P> FromIterator<Pair<T, P>> for syn::punctuated::Punctuated<T, P>

impl<T, P> FromIterator<T> for syn::punctuated::Punctuated<T, P>

where P: Default,

impl<T, P> FromIterator<T> for syn::punctuated::Punctuated<T, P>

where P: Default,

impl<T, S, A> FromIterator<T> for HashSet<T, S, A>

where T: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<T, S, A> FromIterator<T> for HashSet<T, S, A>

where T: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<T, S, A> FromIterator<T> for HashSet<T, S, A>

where T: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

impl<T, S> FromIterator<T> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::collections::HashSet<T, S>

where T: Eq + Hash, S: BuildHasher + Default,

impl<T, S> FromIterator<T> for IndexSet<T, S>

where T: Hash + Eq, S: BuildHasher + Default,

impl<T, U> FromIterator<T> for Array<T, U>

where U: ArraySize,

impl<T, const AMOUNT_OF_BINS: usize, const BIN_OFFSET: u32> FromIterator<T> for AppendOnlyVec<T, AMOUNT_OF_BINS, BIN_OFFSET>

impl<T> FromIterator<(HeaderName, T)> for rama::http::HeaderMap<T>

impl<T> FromIterator<(HeaderName, T)> for HeaderMap<T>

impl<T> FromIterator<(usize, T)> for Slab<T>

Create a slab from an iterator of key-value pairs.

If the iterator produces duplicate keys, the previous value is replaced with the later one. The keys does not need to be sorted beforehand, and this function always takes O(n) time. Note that the returned slab will use space proportional to the largest key, so don’t use Slab with untrusted keys.

Examples

let vec = vec![(2,'a'), (6,'b'), (7,'c')];
let slab = vec.into_iter().collect::<Slab<char>>();
assert_eq!(slab.len(), 3);
assert!(slab.capacity() >= 8);
assert_eq!(slab[2], 'a');

With duplicate and unsorted keys:

let vec = vec![(20,'a'), (10,'b'), (11,'c'), (10,'d')];
let slab = vec.into_iter().collect::<Slab<char>>();
assert_eq!(slab.len(), 3);
assert_eq!(slab[10], 'd');

impl<T> FromIterator<T> for AHashSet<T>

where T: Eq + Hash,

impl<T> FromIterator<T> for AnyValue

where T: Into<AnyValue>,

impl<T> FromIterator<T> for Arc<[T]>

Available on non-no_global_oom_handling only.

impl<T> FromIterator<T> for BTreeSet<T>

where T: Ord,

impl<T> FromIterator<T> for BinaryHeap<T>

where T: Ord,

impl<T> FromIterator<T> for ByteRecord

where T: AsRef<[u8]>,

impl<T> FromIterator<T> for LinkedList<T>

impl<T> FromIterator<T> for Rc<[T]>

Available on non-no_global_oom_handling only.

impl<T> FromIterator<T> for SequenceOf<T>

impl<T> FromIterator<T> for SetOf<T>

impl<T> FromIterator<T> for SourceList

where T: Into<SourceExpression>,

impl<T> FromIterator<T> for StringRecord

where T: AsRef<str>,

impl<T> FromIterator<T> for serde_json::value::Value

where T: Into<Value>,

impl<T> FromIterator<T> for rama::ttrpc::protobuf::prost::alloc::vec::Vec<T>

Available on non-no_global_oom_handling only.

Collects an iterator into a Vec, commonly called via Iterator::collect()

Allocation behavior

In general Vec does not guarantee any particular growth or allocation strategy. That also applies to this trait impl.

Note: This section covers implementation details and is therefore exempt from stability guarantees.

Vec may use any or none of the following strategies, depending on the supplied iterator:

• preallocate based on Iterator::size_hint()
  • and panic if the number of items is outside the provided lower/upper bounds
• use an amortized growth strategy similar to pushing one item at a time
• perform the iteration in-place on the original allocation backing the iterator

The last case warrants some attention. It is an optimization that in many cases reduces peak memory consumption and improves cache locality. But when big, short-lived allocations are created, only a small fraction of their items get collected, no further use is made of the spare capacity and the resulting Vec is moved into a longer-lived structure, then this can lead to the large allocations having their lifetimes unnecessarily extended which can result in increased memory footprint.

In cases where this is an issue, the excess capacity can be discarded with Vec::shrink_to(), Vec::shrink_to_fit() or by collecting into Box<[T]> instead, which additionally reduces the size of the long-lived struct.

static LONG_LIVED: Mutex<Vec<Vec<u16>>> = Mutex::new(Vec::new());

for i in 0..10 {
    let big_temporary: Vec<u16> = (0..1024).collect();
    // discard most items
    let mut result: Vec<_> = big_temporary.into_iter().filter(|i| i % 100 == 0).collect();
    // without this a lot of unused capacity might be moved into the global
    result.shrink_to_fit();
    LONG_LIVED.lock().unwrap().push(result);
}

impl<T> FromIterator<T> for Vec<T>

Available on non-no_global_oom_handling only.

impl<T> FromIterator<T> for VecDeque<T>

impl<U, V> FromIterator<V> for Mean<U>

where U: UnitTag, V: Into<f64>,

impl<V, const N: usize> FromIterator<V> for Distribution<V, N>

where V: MetricValue,

impl<V> FromIterator<V> for Array

where V: Into<Value>,

impl<V> FromIterator<V> for Value

where V: Into<Value>,