once.rs.html -- source

Files

array_init

bitflags

byteorder

cfg_if

futures_channel

mpsc

mod.rs queue.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

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

lib.rs never.rs

gio

auto

action.rs action_group.rs action_map.rs app_info.rs app_info_monitor.rs app_launch_context.rs application.rs application_command_line.rs buffered_input_stream.rs buffered_output_stream.rs bytes_icon.rs cancellable.rs charset_converter.rs constants.rs converter.rs converter_input_stream.rs converter_output_stream.rs credentials.rs data_input_stream.rs data_output_stream.rs desktop_app_info.rs drive.rs emblem.rs emblemed_icon.rs enums.rs file.rs file_attribute_matcher.rs file_enumerator.rs file_icon.rs file_info.rs file_input_stream.rs file_io_stream.rs file_monitor.rs file_output_stream.rs filename_completer.rs filter_input_stream.rs filter_output_stream.rs flags.rs functions.rs icon.rs inet_address.rs inet_address_mask.rs inet_socket_address.rs input_stream.rs io_stream.rs loadable_icon.rs memory_input_stream.rs memory_output_stream.rs menu.rs menu_attribute_iter.rs menu_item.rs menu_link_iter.rs menu_model.rs mod.rs mount.rs mount_operation.rs network_address.rs network_monitor.rs network_service.rs notification.rs output_stream.rs permission.rs pollable_input_stream.rs pollable_output_stream.rs property_action.rs proxy.rs proxy_address.rs proxy_resolver.rs remote_action_group.rs resolver.rs resource.rs seekable.rs settings.rs settings_backend.rs settings_schema.rs settings_schema_key.rs settings_schema_source.rs simple_action.rs simple_action_group.rs simple_permission.rs socket.rs socket_address.rs socket_address_enumerator.rs socket_client.rs socket_connectable.rs socket_connection.rs socket_listener.rs socket_service.rs srv_target.rs subprocess.rs subprocess_launcher.rs tcp_connection.rs themed_icon.rs threaded_socket_service.rs tls_certificate.rs tls_client_connection.rs tls_connection.rs tls_database.rs tls_file_database.rs tls_interaction.rs tls_password.rs tls_server_connection.rs unix_input_stream.rs unix_output_stream.rs unix_socket_address.rs vfs.rs volume.rs volume_monitor.rs zlib_compressor.rs zlib_decompressor.rs

subclass

application.rs input_stream.rs io_stream.rs mod.rs output_stream.rs seekable.rs

gio_sys

glib

glib_sys

lib.rs manual.rs

gobject_sys

gstreamer

allocation_params.rs allocator.rs bin.rs buffer.rs buffer_pool.rs buffer_serde.rs bufferlist.rs bufferlist_serde.rs bus.rs bus_unix.rs bus_windows.rs caps.rs caps_features.rs caps_features_serde.rs caps_serde.rs child_proxy.rs clock.rs clock_time.rs clock_time_serde.rs context.rs date_time.rs date_time_serde.rs device_monitor.rs device_provider.rs element.rs enums.rs error.rs event.rs format.rs format_serde.rs functions.rs ghost_pad.rs gobject.rs iterator.rs lib.rs log.rs memory.rs message.rs meta.rs miniobject.rs object.rs pad.rs pad_template.rs param_spec.rs parse_context.rs pipeline.rs plugin.rs plugin_feature.rs promise.rs proxy_pad.rs query.rs sample.rs sample_serde.rs segment.rs segment_serde.rs static_caps.rs static_pad_template.rs stream.rs stream_collection.rs structure.rs structure_serde.rs tag_setter.rs tags.rs tags_serde.rs toc.rs toc_serde.rs typefind.rs utils.rs value.rs value_serde.rs

gstreamer_app

auto

app_sink.rs app_src.rs enums.rs mod.rs

app_sink.rs app_src.rs lib.rs

gstreamer_app_sys

gstreamer_audio

gstreamer_audio_sys

gstreamer_base

gstreamer_base_sys

gstreamer_check

auto

mod.rs test_clock.rs

harness.rs lib.rs test_clock.rs

gstreamer_check_sys

gstreamer_editing_services

gstreamer_editing_services_sys

gstreamer_gl

gstreamer_gl_sys

lib.rs manual.rs

gstreamer_net

auto

mod.rs net_client_clock.rs net_time_provider.rs ntp_clock.rs ptp_clock.rs

lib.rs net_address_meta.rs net_client_clock.rs net_time_provider.rs ntp_clock.rs ptp_clock.rs

gstreamer_net_sys

gstreamer_pbutils

gstreamer_pbutils_sys

gstreamer_player

gstreamer_player_sys

gstreamer_rtp

auto

constants.rs enums.rs flags.rs functions.rs mod.rs

lib.rs rtp_buffer.rs

gstreamer_rtp_sys

gstreamer_rtsp

auto

enums.rs flags.rs mod.rs rtsp_auth_param.rs rtsp_url.rs

gstreamer_rtsp_server

gstreamer_rtsp_server_sys

gstreamer_rtsp_sys

gstreamer_sdp

auto

lib.rs sdp_attribute.rs sdp_bandwidth.rs sdp_connection.rs sdp_key.rs sdp_media.rs sdp_message.rs sdp_origin.rs sdp_time.rs sdp_zone.rs

gstreamer_sdp_sys

gstreamer_sys

gstreamer_video

gstreamer_video_sys

gstreamer_webrtc

auto

enums.rs mod.rs web_rtc_session_description.rs web_rtcdtls_transport.rs web_rtcice_transport.rs web_rtcrtp_receiver.rs web_rtcrtp_sender.rs web_rtcrtp_transceiver.rs

lib.rs web_rtc_session_description.rs

gstreamer_webrtc_sys

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

muldiv

num_integer

lib.rs roots.rs

num_rational

num_traits

ops

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

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

paste

paste_impl

enum_hack.rs lib.rs

pin_utils

lib.rs projection.rs stack_pin.rs

proc_macro2

detection.rs fallback.rs lib.rs strnom.rs wrapper.rs

proc_macro_hack

error.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

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

impls.rs impossible.rs mod.rs

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

serde_bytes

bytebuf.rs bytes.rs de.rs lib.rs ser.rs

serde_derive

internals

ast.rs attr.rs case.rs check.rs ctxt.rs mod.rs symbol.rs

bound.rs de.rs dummy.rs fragment.rs lib.rs pretend.rs ser.rs try.rs

slab

syn

unicode_xid

lib.rs tables.rs

use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
use pin_utils::unsafe_pinned;

/// Creates a stream of a single element.
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::stream::{self, StreamExt};
///
/// let stream = stream::once(async { 17 });
/// let collected = stream.collect::<Vec<i32>>().await;
/// assert_eq!(collected, vec![17]);
/// # });
/// ```
pub fn once<Fut: Future>(future: Fut) -> Once<Fut> {
    Once { future: Some(future) }
}

/// A stream which emits single element and then EOF.
///
/// This stream will never block and is always ready.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Once<Fut> {
    future: Option<Fut>
}

impl<Fut: Unpin> Unpin for Once<Fut> {}

impl<Fut> Once<Fut> {
    unsafe_pinned!(future: Option<Fut>);
}

impl<Fut: Future> Stream for Once<Fut> {
    type Item = Fut::Output;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let v = match self.as_mut().future().as_pin_mut() {
            Some(fut) => ready!(fut.poll(cx)),
            None => return Poll::Ready(None),
        };

        self.as_mut().future().set(None);
        Poll::Ready(Some(v))
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        if self.future.is_some() {
            (1, Some(1))
        } else {
            (0, Some(0))
        }
    }
}

impl<Fut: Future> FusedStream for Once<Fut> {
    fn is_terminated(&self) -> bool {
        self.future.is_none()
    }
}

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