pub trait Stream {
type Item;
// Required method
fn next(&mut self) -> impl Future<Output = Option<Self::Item>>;
// Provided method
fn size_hint(&self) -> (usize, Option<usize>) { ... }
}Expand description
A stream of values produced asynchronously in pure async/await.
Required Associated Types§
Required Methods§
Provided Methods§
Sourcefn size_hint(&self) -> (usize, Option<usize>)
fn size_hint(&self) -> (usize, Option<usize>)
Returns the bounds on the remaining length of the stream.
Specifically, size_hint() returns a tuple where the first element
is the lower bound, and the second element is the upper bound.
The second half of the tuple that is returned is an
Option<usize>. A None here means that either there
is no known upper bound, or the upper bound is larger than
usize.
§Implementation notes
It is not enforced that a stream implementation yields the declared number of elements. A buggy stream may yield less than the lower bound or more than the upper bound of elements.
size_hint() is primarily intended to be used for optimizations such as
reserving space for the elements of the stream, but must not be
trusted to e.g., omit bounds checks in unsafe code. An incorrect
implementation of size_hint() should not lead to memory safety
violations.
That said, the implementation should provide a correct estimation, because otherwise it would be a violation of the trait’s protocol.
The default implementation returns (0, None) which is correct
for any stream.
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.