once.rs.html -- source

Files

anyhow

backtrace.rs chain.rs context.rs error.rs fmt.rs kind.rs lib.rs macros.rs wrapper.rs

byteorder

bytes

buf

buf_impl.rs buf_mut.rs chain.rs iter.rs limit.rs mod.rs reader.rs take.rs uninit_slice.rs vec_deque.rs writer.rs

fmt

debug.rs hex.rs mod.rs

bytes.rs bytes_mut.rs lib.rs loom.rs

cfg_if

compress

bwt

dc.rs mod.rs mtf.rs

checksum

entropy

ari

apm.rs bin.rs mod.rs table.rs

flate.rs lib.rs lz4.rs rle.rs zlib.rs

derivative

ast.rs attr.rs bound.rs clone.rs cmp.rs debug.rs default.rs hash.rs lib.rs matcher.rs paths.rs utils.rs

futures

futures_channel

mpsc

mod.rs queue.rs sink_impl.rs

lib.rs lock.rs oneshot.rs

futures_core

task

__internal

atomic_waker.rs mod.rs

future.rs lib.rs stream.rs

futures_executor

enter.rs lib.rs local_pool.rs

futures_io

futures_macro

join.rs lib.rs select.rs

futures_sink

futures_task

arc_wake.rs future_obj.rs lib.rs noop_waker.rs spawn.rs waker.rs waker_ref.rs

futures_util

async_await

join_mod.rs mod.rs pending.rs poll.rs random.rs select_mod.rs

future

io

lock

bilock.rs mod.rs mutex.rs

sink

buffer.rs close.rs drain.rs err_into.rs fanout.rs flush.rs map_err.rs mod.rs send.rs send_all.rs with.rs with_flat_map.rs

stream

task

mod.rs spawn.rs

fns.rs lib.rs never.rs

getrandom

error.rs error_impls.rs lib.rs linux_android.rs use_file.rs util.rs util_libc.rs

instant

lib.rs native.rs

lazy_static

inline_lazy.rs lib.rs

libc

unix

linux_like

linux

gnu

b64

x86_64

align.rs mod.rs not_x32.rs

align.rs mod.rs

align.rs mod.rs

align.rs mod.rs

fixed_width_ints.rs lib.rs macros.rs

lock_api

lib.rs mutex.rs remutex.rs rwlock.rs

log

lib.rs macros.rs

memchr

x86

avx.rs mod.rs sse2.rs

fallback.rs iter.rs lib.rs naive.rs

mio

event

event.rs events.rs mod.rs source.rs

macros

net

tcp

listener.rs mod.rs socket.rs stream.rs

uds

datagram.rs listener.rs mod.rs stream.rs

sys

unix

selector

epoll.rs mod.rs

uds

datagram.rs listener.rs mod.rs socketaddr.rs stream.rs

mod.rs net.rs sourcefd.rs tcp.rs udp.rs waker.rs

interest.rs io_source.rs lib.rs poll.rs token.rs waker.rs

num

num_bigint

algorithms.rs bigint.rs biguint.rs lib.rs macros.rs monty.rs

num_complex

cast.rs lib.rs pow.rs

num_cpus

lib.rs linux.rs

num_enum

num_enum_derive

num_integer

average.rs lib.rs roots.rs

num_iter

num_rational

num_traits

ops

checked.rs inv.rs mod.rs mul_add.rs overflowing.rs saturating.rs wrapping.rs

bounds.rs cast.rs float.rs identities.rs int.rs lib.rs macros.rs pow.rs real.rs sign.rs

once_cell

imp_std.rs lib.rs

parking_lot

condvar.rs deadlock.rs elision.rs fair_mutex.rs lib.rs mutex.rs once.rs raw_fair_mutex.rs raw_mutex.rs raw_rwlock.rs remutex.rs rwlock.rs util.rs

parking_lot_core

thread_parker

linux.rs mod.rs

lib.rs parking_lot.rs spinwait.rs util.rs word_lock.rs

pin_project

pin_project_internal

pin_project

args.rs attribute.rs derive.rs mod.rs

lib.rs pinned_drop.rs utils.rs

pin_project_lite

pin_utils

lib.rs projection.rs stack_pin.rs

ppv_lite86

x86_64

lib.rs soft.rs types.rs

proc_macro2

detection.rs fallback.rs lib.rs marker.rs parse.rs wrapper.rs

proc_macro_crate

proc_macro_hack

error.rs iter.rs lib.rs parse.rs quote.rs

proc_macro_nested

quote

ext.rs format.rs ident_fragment.rs lib.rs runtime.rs spanned.rs to_tokens.rs

rand

rand_chacha

chacha.rs guts.rs lib.rs

rand_core

block.rs error.rs impls.rs le.rs lib.rs os.rs

scopeguard

scylla

frame

request

execute.rs mod.rs options.rs prepare.rs query.rs startup.rs

response

cql_to_rust.rs error.rs mod.rs result.rs supported.rs

mod.rs types.rs value.rs

statement

mod.rs prepared_statement.rs query.rs

transport

connection.rs iterator.rs mod.rs session.rs topology.rs

lib.rs macros.rs routing.rs

scylla_macros

serde

de

from_primitive.rs ignored_any.rs impls.rs mod.rs utf8.rs value.rs

private

de.rs macros.rs mod.rs ser.rs

ser

fmt.rs impls.rs impossible.rs mod.rs

export.rs integer128.rs lib.rs macros.rs

signal_hook_registry

half_lock.rs lib.rs

slab

smallvec

snappy

snappy_sys

syn

tokio

fs

future

block_on.rs maybe_done.rs mod.rs poll_fn.rs ready.rs try_join.rs

io

loom

std

atomic_ptr.rs atomic_u16.rs atomic_u32.rs atomic_u64.rs atomic_u8.rs atomic_usize.rs mod.rs mutex.rs parking_lot.rs unsafe_cell.rs

macros

cfg.rs join.rs loom.rs mod.rs pin.rs ready.rs scoped_tls.rs select.rs support.rs thread_local.rs try_join.rs

net

park

either.rs mod.rs thread.rs

process

unix

driver.rs mod.rs orphan.rs reap.rs

runtime

signal

unix

ctrl_c.rs mod.rs registry.rs unix.rs

stream

sync

mpsc

block.rs bounded.rs chan.rs error.rs list.rs mod.rs unbounded.rs

task

atomic_waker.rs mod.rs

barrier.rs batch_semaphore.rs broadcast.rs mod.rs mutex.rs notify.rs oneshot.rs rwlock.rs semaphore.rs watch.rs

task

blocking.rs local.rs mod.rs spawn.rs task_local.rs yield_now.rs

time

driver

atomic_stack.rs entry.rs handle.rs mod.rs

wheel

level.rs mod.rs stack.rs

clock.rs error.rs instant.rs interval.rs mod.rs sleep.rs timeout.rs

util

bit.rs linked_list.rs mod.rs rand.rs slab.rs trace.rs try_lock.rs wake.rs

blocking.rs coop.rs lib.rs prelude.rs

tokio_macros

entry.rs lib.rs select.rs

toml

datetime.rs de.rs lib.rs macros.rs map.rs ser.rs spanned.rs tokens.rs value.rs

unicode_xid

lib.rs tables.rs

uuid

adapter

builder

error.rs mod.rs

parser

error.rs mod.rs

error.rs lib.rs prelude.rs

use crate::stream::{self, Iter, Stream};

use core::option;
use core::pin::Pin;
use core::task::{Context, Poll};

/// Stream for the [`once`](fn@once) function.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Once<T> {
    iter: Iter<option::IntoIter<T>>,
}

impl<I> Unpin for Once<I> {}

/// Creates a stream that emits an element exactly once.
///
/// The returned stream is immediately ready and emits the provided value once.
///
/// # Examples
///
/// ```
/// use tokio::stream::{self, StreamExt};
///
/// #[tokio::main]
/// async fn main() {
///     // one is the loneliest number
///     let mut one = stream::once(1);
///
///     assert_eq!(Some(1), one.next().await);
///
///     // just one, that's all we get
///     assert_eq!(None, one.next().await);
/// }
/// ```
pub fn once<T>(value: T) -> Once<T> {
    Once {
        iter: stream::iter(Some(value).into_iter()),
    }
}

impl<T> Stream for Once<T> {
    type Item = T;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
        Pin::new(&mut self.iter).poll_next(cx)
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

Keyboard Shortcuts

?: Show this help dialog
S: Focus the search field
↑: Move up in search results
↓: Move down in search results
↹: Switch tab
⏎: Go to active search result
+: Expand all sections
-: Collapse all sections

Search Tricks

Prefix searches with a type followed by a colon (e.g., fn:) to restrict the search to a given type.

Accepted types are: fn, mod, struct, enum, trait, type, macro, and const.

Search functions by type signature (e.g., vec -> usize or * -> vec)

Search multiple things at once by splitting your query with comma (e.g., str,u8 or String,struct:Vec,test)

You can look for items with an exact name by putting double quotes around your request: "string"

Look for items inside another one by searching for a path: vec::Vec