Trait scale_info::prelude::iter::FromIterator
1.0.0 · source · 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]);
Object Safety§
Implementors§
impl FromIterator<char> for Box<str>
impl FromIterator<char> for String
impl FromIterator<u8> for Bytes
impl FromIterator<u8> for BytesMut
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<String> for Box<str>
impl FromIterator<String> for String
impl FromIterator<OsString> for OsString
impl<'a> FromIterator<&'a char> for Box<str>
impl<'a> FromIterator<&'a char> for String
impl<'a> FromIterator<&'a str> for Box<str>
impl<'a> FromIterator<&'a str> for String
impl<'a> FromIterator<&'a u8> for BytesMut
impl<'a> FromIterator<&'a OsStr> for OsString
impl<'a> FromIterator<Cow<'a, str>> for Box<str>
impl<'a> FromIterator<Cow<'a, str>> for String
impl<'a> FromIterator<Cow<'a, OsStr>> for OsString
impl<'a> FromIterator<char> for Cow<'a, str>
impl<'a> FromIterator<String> for Cow<'a, str>
impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
impl<'a, M, T1, T2, O1, O2> FromIterator<BitRef<'a, M, T2, O2>> for BitVec<T1, O1>
§Bit-Vector Collection from Proxy References
DO NOT use this. You clearly have a bit-slice. Use
::from_bitslice()
instead!
Iterating over a bit-slice requires loading from memory and constructing a proxy reference for each bit. This is needlessly slow; the specialized method is able to avoid this per-bit cost and possibly even use batched operations.
impl<'a, T> FromIterator<T> for Cow<'a, [T]>where
T: Clone,
impl<'a, T, O> FromIterator<&'a bool> for BitVec<T, O>
impl<'a, T, O> FromIterator<&'a T> for BitVec<T, O>
impl<A> FromIterator<Box<str, A>> for Box<str>where
A: Allocator,
impl<A> FromIterator<Box<str, A>> for Stringwhere
A: Allocator,
impl<A, B, AE, BE> FromIterator<(AE, BE)> for (A, B)
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";
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<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<I> FromIterator<I> for Box<[I]>
impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V>where
K: Ord,
impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
impl<P> FromIterator<P> for PathBuf
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]>
impl<T> FromIterator<T> for Arc<[T]>
impl<T> FromIterator<T> for Vec<T>
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, O> FromIterator<bool> for BitVec<T, O>
§Bit-Vector Collection
This collects a bit-vector from anything that produces individual bits.
§Original
impl<T> FromIterator<T> for Vec<T>
§Notes
This .collect()
call is the second-slowest possible way to collect bits into a
bit-vector, faster only than calling iter.for_each(|bit| bv.push(bit))
.
DO NOT use this if you have any other choice.
If you are collecting a bit-vector from the contents of a bit-slice, then you
should use ::from_bitslice()
instead. That method is specialized to
perform upfront allocation and, where possible, use a batch copy rather than
copying each bit individually from the source into the bit-vector.
impl<T, O> FromIterator<T> for BitVec<T, O>
impl<T, O, I> FromIterator<I> for BitBox<T, O>
impl<T, S> FromIterator<T> for HashSet<T, S>
impl<T, const CAP: usize> FromIterator<T> for ArrayVec<T, CAP>
Create an ArrayVec
from an iterator.
Panics if the number of elements in the iterator exceeds the arrayvec’s capacity.