lazy.rs.html -- source

Files

anyhow

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

async_stream

async_stream.rs lib.rs next.rs yielder.rs

async_stream_impl

async_trait

args.rs expand.rs lib.rs lifetime.rs parse.rs receiver.rs

base64

write

encoder.rs mod.rs

chunked_encoder.rs decode.rs display.rs encode.rs lib.rs tables.rs

byteorder

bytes

buf

ext

chain.rs limit.rs mod.rs reader.rs take.rs writer.rs

buf_impl.rs buf_mut.rs iter.rs mod.rs vec_deque.rs

fmt

debug.rs hex.rs mod.rs

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

cfg_if

either

firestore_grpc

firestore_grpc_cloudrun

compute_metadata.rs lib.rs

fnv

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

lib.rs never.rs

getrandom

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

h2

http

header

map.rs mod.rs name.rs value.rs

uri

authority.rs builder.rs mod.rs path.rs port.rs scheme.rs

byte_str.rs convert.rs error.rs extensions.rs lib.rs method.rs request.rs response.rs status.rs version.rs

http_body

lib.rs next.rs size_hint.rs

httparse

simd

avx2.rs mod.rs sse42.rs

iter.rs lib.rs macros.rs

hyper

body

aggregate.rs body.rs mod.rs payload.rs to_bytes.rs

client

connect

dns.rs http.rs mod.rs

conn.rs dispatch.rs mod.rs pool.rs service.rs

common

io

mod.rs rewind.rs

buf.rs drain.rs exec.rs lazy.rs mod.rs never.rs task.rs watch.rs

proto

h1

conn.rs date.rs decode.rs dispatch.rs encode.rs io.rs mod.rs role.rs

h2

bdp.rs client.rs mod.rs server.rs

server

accept.rs conn.rs mod.rs shutdown.rs tcp.rs

service

http.rs make.rs mod.rs oneshot.rs util.rs

error.rs headers.rs lib.rs rt.rs upgrade.rs

indexmap

equivalent.rs lib.rs macros.rs map.rs mutable_keys.rs set.rs util.rs

iovec

sys

itertools

itoa

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

log

lib.rs macros.rs

memchr

x86

avx.rs mod.rs sse2.rs

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

mio

net2

sys

unix

impls.rs mod.rs

ext.rs lib.rs socket.rs tcp.rs udp.rs unix.rs utils.rs

openssl_probe

percent_encoding

pin_project

pin_project_internal

pin_project

attribute.rs derive.rs mod.rs

lib.rs pinned_drop.rs project.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

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

proc_macro_hack

proc_macro_nested

prost

encoding.rs error.rs lib.rs message.rs types.rs

prost_derive

field

group.rs map.rs message.rs mod.rs oneof.rs scalar.rs

prost_types

compiler.rs lib.rs protobuf.rs

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

rand_pcg

lib.rs pcg128.rs pcg64.rs

ring

rustls

rustls_native_certs

lib.rs linux.rs

ryu

buffer

pretty

exponent.rs mantissa.rs mod.rs

common.rs d2s.rs d2s_full_table.rs d2s_intrinsics.rs digit_table.rs f2s.rs lib.rs

sct

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_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

serde_json

features_check

io

value

de.rs from.rs index.rs mod.rs partial_eq.rs ser.rs

de.rs error.rs iter.rs lib.rs macros.rs map.rs number.rs read.rs ser.rs

slab

spin

lib.rs mutex.rs once.rs rw_lock.rs

syn

time

display.rs duration.rs lib.rs parse.rs sys.rs

tokio

future

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

io

loom

std

alloc.rs atomic_u32.rs atomic_u64.rs atomic_usize.rs causal_cell.rs mod.rs

macros

cfg.rs loom.rs mod.rs pin.rs ready.rs support.rs thread_local.rs

net

tcp

incoming.rs listener.rs mod.rs split.rs stream.rs

park

either.rs mod.rs thread.rs

runtime

blocking

mod.rs pool.rs schedule.rs shutdown.rs task.rs

basic_scheduler.rs builder.rs context.rs enter.rs handle.rs io.rs mod.rs shell.rs spawner.rs time.rs

sync

mpsc

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

task

atomic_waker.rs mod.rs

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

task

blocking.rs core.rs error.rs harness.rs join.rs list.rs mod.rs queue.rs raw.rs spawn.rs stack.rs state.rs waker.rs yield_now.rs

time

driver

atomic_stack.rs entry.rs handle.rs mod.rs registration.rs stack.rs

wheel

level.rs mod.rs stack.rs

clock.rs delay.rs delay_queue.rs error.rs instant.rs interval.rs mod.rs timeout.rs

util

slab

addr.rs entry.rs generation.rs mod.rs page.rs shard.rs slot.rs stack.rs

bit.rs linked_list.rs mod.rs

lib.rs prelude.rs

tokio_rustls

common

handshake.rs mod.rs

client.rs lib.rs server.rs

tokio_util

codec

bytes_codec.rs decoder.rs encoder.rs framed.rs framed_read.rs framed_write.rs length_delimited.rs lines_codec.rs mod.rs

tonic

client

grpc.rs mod.rs service.rs

codec

buffer.rs decode.rs encode.rs mod.rs prost.rs

metadata

encoding.rs key.rs map.rs mod.rs value.rs

server

grpc.rs mod.rs service.rs

transport

channel

endpoint.rs mod.rs tls.rs

server

conn.rs incoming.rs mod.rs tls.rs

service

add_origin.rs connection.rs connector.rs discover.rs io.rs layer.rs mod.rs reconnect.rs router.rs tls.rs

error.rs mod.rs tls.rs

body.rs codegen.rs interceptor.rs lib.rs macros.rs request.rs response.rs status.rs

tower

builder

tower_balance

p2c

layer.rs make.rs mod.rs service.rs

pool

error.rs lib.rs

tower_buffer

error.rs future.rs layer.rs lib.rs message.rs service.rs worker.rs

tower_discover

error.rs lib.rs list.rs stream.rs

tower_layer

identity.rs lib.rs stack.rs

tower_limit

concurrency

sync

cell.rs mod.rs semaphore.rs waker.rs

future.rs layer.rs mod.rs service.rs

rate

layer.rs mod.rs rate.rs service.rs

tower_load

constant.rs instrument.rs lib.rs peak_ewma.rs pending_requests.rs

tower_load_shed

error.rs future.rs layer.rs lib.rs

tower_make

lib.rs make_connection.rs make_service.rs

tower_ready_cache

cache.rs error.rs lib.rs

tower_retry

budget.rs future.rs layer.rs lib.rs policy.rs

tower_service

tower_timeout

error.rs future.rs layer.rs lib.rs

tower_util

boxed

mod.rs sync.rs unsync.rs

call_all

common.rs mod.rs ordered.rs unordered.rs

optional

error.rs future.rs mod.rs

either.rs lib.rs oneshot.rs ready.rs service_fn.rs

tracing

dispatcher.rs field.rs level_filters.rs lib.rs macros.rs span.rs stdlib.rs subscriber.rs

tracing_attributes

tracing_core

callsite.rs dispatcher.rs event.rs field.rs lib.rs metadata.rs parent.rs span.rs stdlib.rs subscriber.rs

tracing_futures

executor

lib.rs stdlib.rs

try_lock

unicode_xid

lib.rs tables.rs

untrusted

want

webpki

calendar.rs cert.rs der.rs error.rs name.rs signed_data.rs time.rs trust_anchor_util.rs verify_cert.rs webpki.rs

use core::pin::Pin;
use futures_core::future::{FusedFuture, Future};
use futures_core::task::{Context, Poll};

/// Future for the [`lazy`] function.
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct Lazy<F> {
    f: Option<F>
}

// safe because we never generate `Pin<&mut F>`
impl<F> Unpin for Lazy<F> {}

/// Creates a new future that allows delayed execution of a closure.
///
/// The provided closure is only run once the future is polled.
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::future;
///
/// let a = future::lazy(|_| 1);
/// assert_eq!(a.await, 1);
///
/// let b = future::lazy(|_| -> i32 {
///     panic!("oh no!")
/// });
/// drop(b); // closure is never run
/// # });
/// ```
pub fn lazy<F, R>(f: F) -> Lazy<F>
    where F: FnOnce(&mut Context<'_>) -> R,
{
    Lazy { f: Some(f) }
}

impl<F, R> FusedFuture for Lazy<F>
    where F: FnOnce(&mut Context<'_>) -> R,
{
    fn is_terminated(&self) -> bool { self.f.is_none() }
}

impl<F, R> Future for Lazy<F>
    where F: FnOnce(&mut Context<'_>) -> R,
{
    type Output = R;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<R> {
        Poll::Ready((self.f.take().unwrap())(cx))
    }
}

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