Trait nom::lib::std::iter::FromIterator

[+] Show declaration

pub trait FromIterator<A> {
    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.

FromIterator::from_iter() is rarely called explicitly, and is instead used through Iterator::collect() method. See Iterator::collect()'s documentation for more examples.

See also: IntoIterator.

Examples

Basic usage:

use std::iter::FromIterator;

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]);

Implementing FromIterator for your type:

use std::iter::FromIterator;

// 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

Basic usage:

use std::iter::FromIterator;

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]);

Implementations on Foreign Types

impl<P> FromIterator<P> for PathBuf where
    P: AsRef<Path>, [−]

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fn from_iter<I>(iter: I) -> PathBuf where
    I: IntoIterator<Item = P>, 

impl FromIterator<()> for ()[−]

[−] Expand description

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());

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fn from_iter<I>(iter: I) where
    I: IntoIterator<Item = ()>, 

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

fn from_iter<I>(iter: I) -> Rc<[T]> where
    I: IntoIterator<Item = T>, [−]

Takes each element in the Iterator and collects it into an Rc<[T]>.

Performance characteristics

The general case

In the general case, collecting into Rc<[T]> is done by first collecting into a Vec<T>. That is, when writing the following:

let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();

this behaves as if we wrote:

let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
    .collect::<Vec<_>>() // The first set of allocations happens here.
    .into(); // A second allocation for `Rc<[T]>` happens here.

This will allocate as many times as needed for constructing the Vec<T> and then it will allocate once for turning the Vec<T> into the Rc<[T]>.

Iterators of known length

When your Iterator implements TrustedLen and is of an exact size, a single allocation will be made for the Rc<[T]>. For example:

let evens: Rc<[u8]> = (0..10).collect(); // Just a single allocation happens here.

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

fn from_iter<I>(iter: I) -> Arc<[T]> where
    I: IntoIterator<Item = T>, [−]

Takes each element in the Iterator and collects it into an Arc<[T]>.

Performance characteristics

The general case

In the general case, collecting into Arc<[T]> is done by first collecting into a Vec<T>. That is, when writing the following:

let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();

this behaves as if we wrote:

let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
    .collect::<Vec<_>>() // The first set of allocations happens here.
    .into(); // A second allocation for `Arc<[T]>` happens here.

This will allocate as many times as needed for constructing the Vec<T> and then it will allocate once for turning the Vec<T> into the Arc<[T]>.

Iterators of known length

When your Iterator implements TrustedLen and is of an exact size, a single allocation will be made for the Arc<[T]>. For example:

let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here.

Implementors

impl FromIterator<char> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = char>, 

impl FromIterator<Box<str>> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = Box<str>>, 

impl FromIterator<String> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = String>, 

impl<'a> FromIterator<&'a char> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = &'a char>, 

impl<'a> FromIterator<&'a str> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = &'a str>, 

impl<'a> FromIterator<Cow<'a, str>> for String[+]

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fn from_iter<I>(iter: I) -> String where
    I: IntoIterator<Item = Cow<'a, str>>, 

impl<'a> FromIterator<char> for Cow<'a, str>[+]

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fn from_iter<I>(it: I) -> Cow<'a, str> where
    I: IntoIterator<Item = char>, 

impl<'a> FromIterator<String> for Cow<'a, str>[+]

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fn from_iter<I>(it: I) -> Cow<'a, str> where
    I: IntoIterator<Item = String>, 

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

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fn from_iter<I>(it: I) -> Cow<'a, str> where
    I: IntoIterator<Item = &'b str>, 

impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
    T: Clone, [+]

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fn from_iter<I>(it: I) -> Cow<'a, [T]> where
    I: IntoIterator<Item = T>, 

impl<A> FromIterator<A> for VecDeque<A>[+]

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fn from_iter<T>(iter: T) -> VecDeque<A> where
    T: IntoIterator<Item = A>, 

impl<A> FromIterator<A> for Box<[A]>[+]

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fn from_iter<T>(iter: T) -> Box<[A]> where
    T: IntoIterator<Item = A>, 

impl<A, E, V> FromIterator<Result<A, E>> for Result<V, E> where
    V: FromIterator<A>, [+]

fn from_iter<I>(iter: I) -> Result<V, E> where
    I: IntoIterator<Item = Result<A, E>>, [−]

Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, a container with the values of each Result is returned.

Here is an example which increments every integer in a vector, checking for overflow:

let v = vec![1, 2];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
    x.checked_add(1).ok_or("Overflow!")
).collect();
assert_eq!(res, Ok(vec![2, 3]));

Here is another example that tries to subtract one from another list of integers, this time checking for underflow:

let v = vec![1, 2, 0];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
    x.checked_sub(1).ok_or("Underflow!")
).collect();
assert_eq!(res, Err("Underflow!"));

Here is a variation on the previous example, showing that no further elements are taken from iter after the first Err.

let v = vec![3, 2, 1, 10];
let mut shared = 0;
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32| {
    shared += x;
    x.checked_sub(2).ok_or("Underflow!")
}).collect();
assert_eq!(res, Err("Underflow!"));
assert_eq!(shared, 6);

Since the third element caused an underflow, no further elements were taken, so the final value of shared is 6 (= 3 + 2 + 1), not 16.

impl<A, V> FromIterator<Option<A>> for Option<V> where
    V: FromIterator<A>, [+]

fn from_iter<I>(iter: I) -> Option<V> where
    I: IntoIterator<Item = Option<A>>, [−]

Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a container with the values of each Option is returned.

Examples

Here is an example which increments every integer in a vector. We use the checked variant of add that returns None when the calculation would result in an overflow.

let items = vec![0_u16, 1, 2];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_add(1))
    .collect();

assert_eq!(res, Some(vec![1, 2, 3]));

As you can see, this will return the expected, valid items.

Here is another example that tries to subtract one from another list of integers, this time checking for underflow:

let items = vec![2_u16, 1, 0];

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| x.checked_sub(1))
    .collect();

assert_eq!(res, None);

Since the last element is zero, it would underflow. Thus, the resulting value is None.

Here is a variation on the previous example, showing that no further elements are taken from iter after the first None.

let items = vec![3_u16, 2, 1, 10];

let mut shared = 0;

let res: Option<Vec<u16>> = items
    .iter()
    .map(|x| { shared += x; x.checked_sub(2) })
    .collect();

assert_eq!(res, None);
assert_eq!(shared, 6);

Since the third element caused an underflow, no further elements were taken, so the final value of shared is 6 (= 3 + 2 + 1), not 16.

impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V> where
    K: Ord, [+]

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fn from_iter<T>(iter: T) -> BTreeMap<K, V> where
    T: IntoIterator<Item = (K, V)>, 

impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S> where
    K: Eq + Hash,
    S: BuildHasher + Default, [+]

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fn from_iter<T>(iter: T) -> HashMap<K, V, S> where
    T: IntoIterator<Item = (K, V)>, 

impl<T> FromIterator<T> for BTreeSet<T> where
    T: Ord, [+]

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fn from_iter<I>(iter: I) -> BTreeSet<T> where
    I: IntoIterator<Item = T>, 

impl<T> FromIterator<T> for BinaryHeap<T> where
    T: Ord, [+]

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fn from_iter<I>(iter: I) -> BinaryHeap<T> where
    I: IntoIterator<Item = T>, 

impl<T> FromIterator<T> for LinkedList<T>[+]

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fn from_iter<I>(iter: I) -> LinkedList<T> where
    I: IntoIterator<Item = T>, 

impl<T> FromIterator<T> for Vec<T>[+]

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fn from_iter<I>(iter: I) -> Vec<T> where
    I: IntoIterator<Item = T>, 

impl<T, S> FromIterator<T> for HashSet<T, S> where
    S: BuildHasher + Default,
    T: Eq + Hash, [+]

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fn from_iter<I>(iter: I) -> HashSet<T, S> where
    I: IntoIterator<Item = T>, 

impl FromIterator<Sides> for Sides

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

impl<T> FromIterator<Steal<T>> for Steal<T>

impl FromIterator<ColorMask> for ColorMask

impl FromIterator<Mirror> for Mirror

impl FromIterator<usize> for FixedBitSet

impl<F: Future> FromIterator<F> for JoinAll<F>

impl<Fut: Future + Unpin> FromIterator<Fut> for SelectAll<Fut>

impl<F: TryFuture> FromIterator<F> for TryJoinAll<F>

impl<Fut: TryFuture + Unpin> FromIterator<Fut> for SelectOk<Fut>

impl<Fut: Future> FromIterator<Fut> for FuturesOrdered<Fut>

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

impl<St: Stream + Unpin> FromIterator<St> for SelectAll<St>

impl FromIterator<Access> for Access

impl FromIterator<Bind> for Bind

impl FromIterator<Usage> for Usage

impl FromIterator<DepthStencilFlags> for DepthStencilFlags

impl FromIterator<DescriptorSetLayoutBinding> for DescriptorCounts

impl FromIterator<Usage> for Usage

impl FromIterator<Access> for Access

impl FromIterator<CommandBufferFlags> for CommandBufferFlags

impl FromIterator<Aspects> for Aspects

impl FromIterator<ImageFeature> for ImageFeature

impl FromIterator<BufferFeature> for BufferFeature

impl FromIterator<ViewCapabilities> for ViewCapabilities

impl FromIterator<Usage> for Usage

impl FromIterator<Access> for Access

impl FromIterator<Properties> for Properties

impl FromIterator<Dependencies> for Dependencies

impl FromIterator<CommandPoolCreateFlags> for CommandPoolCreateFlags

impl FromIterator<DescriptorPoolCreateFlags> for DescriptorPoolCreateFlags

impl FromIterator<ColorMask> for ColorMask

impl FromIterator<Face> for Face

impl FromIterator<PipelineStage> for PipelineStage

impl FromIterator<ShaderStageFlags> for ShaderStageFlags

impl FromIterator<PipelineCreationFlags> for PipelineCreationFlags

impl FromIterator<ControlFlags> for ControlFlags

impl FromIterator<ResultFlags> for ResultFlags

impl FromIterator<PipelineStatistic> for PipelineStatistic

impl FromIterator<PresentMode> for PresentMode

impl FromIterator<CompositeAlphaMode> for CompositeAlphaMode

impl FromIterator<Features> for Features

impl FromIterator<u32> for BitSet

impl<'a> FromIterator<&'a u32> for BitSet

impl FromIterator<u32> for AtomicBitSet

impl<'a> FromIterator<&'a u32> for AtomicBitSet

impl FromIterator<ModifierKey> for ModifierKey

impl<K: Hash + Eq, V, S: BuildHasher + Default> FromIterator<(K, V)> for LinkedHashMap<K, V, S>

impl FromIterator<WriterFlags> for WriterFlags

impl FromIterator<SamplingFlags> for SamplingFlags

impl FromIterator<ImageFlags> for ImageFlags

impl FromIterator<GlobalUse> for GlobalUse

impl FromIterator<AtFlags> for AtFlags

impl FromIterator<OFlag> for OFlag

impl FromIterator<SealFlag> for SealFlag

impl FromIterator<FdFlag> for FdFlag

impl FromIterator<SpliceFFlags> for SpliceFFlags

impl FromIterator<FallocateFlags> for FallocateFlags

impl FromIterator<ModuleInitFlags> for ModuleInitFlags

impl FromIterator<DeleteModuleFlags> for DeleteModuleFlags

impl FromIterator<MsFlags> for MsFlags

impl FromIterator<MntFlags> for MntFlags

impl FromIterator<MQ_OFlag> for MQ_OFlag

impl FromIterator<FdFlag> for FdFlag

impl FromIterator<InterfaceFlags> for InterfaceFlags

impl FromIterator<PollFlags> for PollFlags

impl FromIterator<CloneFlags> for CloneFlags

impl FromIterator<EpollFlags> for EpollFlags

impl FromIterator<EpollCreateFlags> for EpollCreateFlags

impl FromIterator<EfdFlags> for EfdFlags

impl FromIterator<MemFdCreateFlag> for MemFdCreateFlag

impl FromIterator<ProtFlags> for ProtFlags

impl FromIterator<MapFlags> for MapFlags

impl FromIterator<MsFlags> for MsFlags

impl FromIterator<MlockAllFlags> for MlockAllFlags

impl FromIterator<Options> for Options

impl FromIterator<QuotaValidFlags> for QuotaValidFlags

impl FromIterator<SaFlags> for SaFlags

impl FromIterator<SfdFlags> for SfdFlags

impl FromIterator<SockFlag> for SockFlag

impl FromIterator<MsgFlags> for MsgFlags

impl FromIterator<SFlag> for SFlag

impl FromIterator<Mode> for Mode

impl FromIterator<FsFlags> for FsFlags

impl FromIterator<InputFlags> for InputFlags

impl FromIterator<OutputFlags> for OutputFlags

impl FromIterator<ControlFlags> for ControlFlags

impl FromIterator<LocalFlags> for LocalFlags

impl FromIterator<WaitPidFlag> for WaitPidFlag

impl FromIterator<AddWatchFlags> for AddWatchFlags

impl FromIterator<InitFlags> for InitFlags

impl FromIterator<TimerFlags> for TimerFlags

impl FromIterator<TimerSetTimeFlags> for TimerSetTimeFlags

impl FromIterator<AccessFlags> for AccessFlags

impl<T, S> FromIterator<T> for OrderSet<T, S> where     T: Hash + Eq,     S: BuildHasher + Default,

impl<K, V, S> FromIterator<(K, V)> for OrderMap<K, V, S> where     K: Hash + Eq,     S: BuildHasher + Default,

impl<N, E, Ty, Item> FromIterator<Item> for GraphMap<N, E, Ty> where     Item: IntoWeightedEdge<E, NodeId = N>,     N: NodeTrait,     Ty: EdgeType,

impl FromIterator<TokenTree> for TokenStream

impl FromIterator<TokenStream> for TokenStream

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

impl<T: Into<Value>> FromIterator<T> for Value

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

impl FromIterator<ImageOperands> for ImageOperands

impl FromIterator<FPFastMathMode> for FPFastMathMode

impl FromIterator<SelectionControl> for SelectionControl

impl FromIterator<LoopControl> for LoopControl

impl FromIterator<FunctionControl> for FunctionControl

impl FromIterator<MemorySemantics> for MemorySemantics

impl FromIterator<MemoryAccess> for MemoryAccess

impl FromIterator<KernelProfilingInfo> for KernelProfilingInfo

impl FromIterator<RayFlags> for RayFlags

impl<T, P> FromIterator<T> for Punctuated<T, P> where     P: Default,

impl<T, P> FromIterator<Pair<T, P>> for Punctuated<T, P>

impl FromIterator<CString> for RawDeviceExtensions

impl FromIterator<CString> for RawInstanceExtensions

impl FromIterator<DndAction> for DndAction

impl FromIterator<Resize> for Resize

impl FromIterator<Transient> for Transient

impl FromIterator<Capability> for Capability

impl FromIterator<Mode> for Mode

impl FromIterator<ContentHint> for ContentHint

impl FromIterator<Anchor> for Anchor

impl FromIterator<Gravity> for Gravity

impl FromIterator<ConstraintAdjustment> for ConstraintAdjustment

impl FromIterator<Anchor> for Anchor

impl FromIterator<Flags> for Flags

impl FromIterator<ConstraintAdjustment> for ConstraintAdjustment

impl FromIterator<PipelineFlags> for PipelineFlags

impl FromIterator<BufferUse> for BufferUse

impl FromIterator<TextureUse> for TextureUse

impl FromIterator<BackendBit> for BackendBit

impl FromIterator<Features> for Features

impl FromIterator<ShaderStage> for ShaderStage

impl FromIterator<ColorWrite> for ColorWrite

impl FromIterator<BufferUsage> for BufferUsage

impl FromIterator<TextureUsage> for TextureUsage

impl FromIterator<ModifiersState> for ModifiersState