pub trait FromIterator<A>: Sized {
// Required method
fn from_iter<T>(iter: T) -> Self
where T: IntoIterator<Item = A>;
}Expand description
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§
1.0.0 · Sourcefn from_iter<T>(iter: T) -> Selfwhere
T: IntoIterator<Item = A>,
fn from_iter<T>(iter: T) -> Selfwhere
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", so this trait is not object safe.
Implementors§
impl FromIterator<(Key, (StringValue, BaggageMetadata))> for Baggage
impl FromIterator<(String, Value)> for Map<String, Value>
impl FromIterator<PseudoHeader> for PseudoHeaderOrder
impl FromIterator<SettingId> for SettingOrder
impl FromIterator<AsciiChar> for String
Available on non-
no_global_oom_handling only.impl FromIterator<IpAddr> for XForwardedFor
impl FromIterator<TokenTree> for proc_macro::TokenStream
Collects a number of token trees into a single stream.
impl FromIterator<Weekday> for WeekdaySet
impl FromIterator<TokenTree> for proc_macro2::TokenStream
Collects a number of token trees into a single stream.
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 String
Available on non-
no_global_oom_handling only.impl FromIterator<char> for SmolStr
impl FromIterator<u8> for Bytes
impl FromIterator<u8> for BytesMut
impl FromIterator<u8> for ByteString
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<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 FromIterator<UriMatchReplaceRule> for UriMatchReplaceRuleset
impl FromIterator<KeyValueMetadata> for Baggage
impl FromIterator<KeyValue> for Baggage
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<X509CheckFlags> for X509CheckFlags
impl FromIterator<X509VerifyFlags> for X509VerifyFlags
impl FromIterator<UserAgentProfile> for UserAgentDatabase
impl FromIterator<ByteString> for ByteString
impl FromIterator<String> for rama::utils::collections::smallvec::alloc::boxed::Box<str>
Available on non-
no_global_oom_handling only.impl FromIterator<String> for String
Available on non-
no_global_oom_handling only.impl FromIterator<String> for SmolStr
impl FromIterator<TrustAnchor<'static>> for RootCertStore
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<OsString> for OsString
impl FromIterator<TokenStream> for proc_macro2::TokenStream
impl FromIterator<Access> for Access
impl FromIterator<AtFlags> for AtFlags
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<Literal> for Seq
impl FromIterator<MemfdFlags> for MemfdFlags
impl FromIterator<Mode> for Mode
impl FromIterator<OFlags> for OFlags
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<StatVfsMountFlags> for StatVfsMountFlags
impl FromIterator<StatxAttributes> for StatxAttributes
impl FromIterator<StatxFlags> for StatxFlags
impl FromIterator<Table> for ArrayOfTables
impl FromIterator<ViaElement> for Via
impl FromIterator<WatchFlags> for WatchFlags
impl FromIterator<XattrFlags> for XattrFlags
impl<'a> FromIterator<&'a PseudoHeader> for PseudoHeaderOrder
impl<'a> FromIterator<&'a SettingId> for SettingOrder
impl<'a> FromIterator<&'a AsciiChar> for String
Available on non-
no_global_oom_handling only.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 String
Available on non-
no_global_oom_handling only.impl<'a> FromIterator<&'a str> for SmolStr
impl<'a> FromIterator<&'a u8> for BytesMut
impl<'a> FromIterator<&'a ByteStr> for ByteString
impl<'a> FromIterator<&'a String> for SmolStr
impl<'a> FromIterator<&'a OsStr> for OsString
impl<'a> FromIterator<&'a [u8]> for ByteString
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<Cow<'a, OsStr>> for OsString
impl<'a> FromIterator<AsciiChar> 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> FromIterator<String> for Cow<'a, str>
Available on non-
no_global_oom_handling only.impl<'a> FromIterator<AttributeTypeAndValue<'a>> for RelativeDistinguishedName<'a>
impl<'a> FromIterator<RelativeDistinguishedName<'a>> for X509Name<'a>
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 as Array>::Item> for SmallVec<A>where
A: Array,
impl<A> FromIterator<<A as Array>::Item> for ArrayVec<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 Stringwhere
A: Allocator,
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<F> FromIterator<F> for JoinAll<F>where
F: Future,
impl<F> FromIterator<F> for TryJoinAll<F>where
F: TryFuture,
impl<Fut> FromIterator<Fut> for rama::futures::prelude::future::SelectAll<Fut>
impl<Fut> FromIterator<Fut> for SelectOk<Fut>
impl<Fut> FromIterator<Fut> for FuturesOrdered<Fut>where
Fut: Future,
impl<Fut> FromIterator<Fut> for FuturesUnordered<Fut>
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> FromIterator<(K, V)> for AnyValue
impl<K, V> FromIterator<(K, V)> for serde_json::value::Value
impl<K, V> FromIterator<(K, V)> for UriParams
impl<K, V> FromIterator<(K, V)> for StreamMap<K, V>
impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V>where
K: Ord,
impl<K, V> FromIterator<(K, V)> for AHashMap<K, V>
impl<K, V> FromIterator<(K, V)> for Attributes
Available on crate feature
logs only.impl<K, V> FromIterator<(K, V)> for InlineTable
impl<K, V> FromIterator<(K, V)> for Table
impl<K, V> FromIterator<(K, V)> for Trie<K, V>where
K: TrieKey,
impl<K, V> FromIterator<(K, V)> for Value
impl<K, V, S> FromIterator<(K, Vec<V>)> for MultiMap<K, V, S>
impl<K, V, S> FromIterator<(K, V)> for rama::crypto::dep::x509_parser::prelude::asn1_rs::nom::lib::std::collections::HashMap<K, V, S>
impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>
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>
impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>
impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>
impl<N> FromIterator<(N, HeaderValue)> for Http1HeaderMapwhere
N: IntoHttp1HeaderName,
impl<N> FromIterator<N> for OriginalHttp1Headerswhere
N: IntoHttp1HeaderName,
impl<P> FromIterator<P> for PathBuf
impl<S> FromIterator<S> for SubdomainTrieMatcherwhere
S: AsDomainRef,
impl<S, T> FromIterator<(S, T)> for DomainTrie<T>where
S: AsDomainRef,
impl<St> FromIterator<St> for rama::futures::stream::SelectAll<St>
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<(HeaderName, T)> for HeaderMap<T>
impl<T> FromIterator<T> for AnyValue
impl<T> FromIterator<T> for serde_json::value::Value
impl<T> FromIterator<T> for rama::http::grpc::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
pushingone 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 BTreeSet<T>where
T: Ord,
impl<T> FromIterator<T> for BinaryHeap<T>where
T: Ord,
impl<T> FromIterator<T> for LinkedList<T>
impl<T> FromIterator<T> for VecDeque<T>
impl<T> FromIterator<T> for Rc<[T]>
Available on non-
no_global_oom_handling only.impl<T> FromIterator<T> for Arc<[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 AHashSet<T>
impl<T> FromIterator<T> for ByteRecord
impl<T> FromIterator<T> for StringRecord
impl<T> FromIterator<T> for Vec<T>
Available on non-
no_global_oom_handling only.impl<T, ExtendT> FromIterator<(T₁, T₂, …, Tₙ)> for (ExtendT₁, ExtendT₂, …, ExtendTₙ)
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>
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]);
}