1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93

//! Stream utilities for Tokio.
//!
//! `Stream`s are an asynchoronous version of standard library's Iterator.
//!
//! This module provides helpers to work with them.

mod iter;
pub use iter::{iter, Iter};

mod map;
use map::Map;

mod next;
use next::Next;

pub use futures_core::Stream;

/// An extension trait for `Stream`s that provides a variety of convenient
/// combinator functions.
pub trait StreamExt: Stream {
    /// Creates a future that resolves to the next item in the stream.
    ///
    /// Equivalent to:
    ///
    /// ```ignore
    /// async fn next(&mut self) -> Option<Self::Item>;
    /// ```
    ///
    /// Note that because `next` doesn't take ownership over the stream,
    /// the [`Stream`] type must be [`Unpin`]. If you want to use `next` with a
    /// [`!Unpin`](Unpin) stream, you'll first have to pin the stream. This can
    /// be done by boxing the stream using [`Box::pin`] or
    /// pinning it to the stack using the `pin_mut!` macro from the `pin_utils`
    /// crate.
    ///
    /// # Examples
    ///
    /// ```
    /// # #[tokio::main]
    /// # async fn main() {
    /// use tokio::stream::{self, StreamExt};
    ///
    /// let mut stream = stream::iter(1..=3);
    ///
    /// assert_eq!(stream.next().await, Some(1));
    /// assert_eq!(stream.next().await, Some(2));
    /// assert_eq!(stream.next().await, Some(3));
    /// assert_eq!(stream.next().await, None);
    /// # }
    /// ```
    fn next(&mut self) -> Next<'_, Self>
    where
        Self: Unpin,
    {
        Next::new(self)
    }

    /// Maps this stream's items to a different type, returning a new stream of
    /// the resulting type.
    ///
    /// The provided closure is executed over all elements of this stream as
    /// they are made available. It is executed inline with calls to
    /// [`poll_next`](Stream::poll_next).
    ///
    /// Note that this function consumes the stream passed into it and returns a
    /// wrapped version of it, similar to the existing `map` methods in the
    /// standard library.
    ///
    /// # Examples
    ///
    /// ```
    /// # #[tokio::main]
    /// # async fn main() {
    /// use tokio::stream::{self, StreamExt};
    ///
    /// let stream = stream::iter(1..=3);
    /// let mut stream = stream.map(|x| x + 3);
    ///
    /// assert_eq!(stream.next().await, Some(4));
    /// assert_eq!(stream.next().await, Some(5));
    /// assert_eq!(stream.next().await, Some(6));
    /// # }
    /// ```
    fn map<T, F>(self, f: F) -> Map<Self, F>
    where
        F: FnMut(Self::Item) -> T,
        Self: Sized,
    {
        Map::new(self, f)
    }
}

impl<T: ?Sized> StreamExt for T where T: Stream {}