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Add Stream::size_hint #1853

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merged 1 commit into from Sep 3, 2019
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taiki-e
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@taiki-e taiki-e commented Sep 1, 2019

@@ -126,7 +165,7 @@ mod private_try_stream {

/// A convenience for streams that return `Result` values that includes
/// a variety of adapters tailored to such futures.
pub trait TryStream: private_try_stream::Sealed {
pub trait TryStream: Stream + private_try_stream::Sealed {
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Added this bound because it would be convenient if stream.size_hint() could be called on St: TryStream.

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oh...

error[E0191]: the value of the associated type `Item` (from the trait `futures_core::stream::Stream`) must be specified
  --> futures/tests/object_safety.rs:20:30
   |
20 |     assert_is_object_safe::<&dyn TryStream<Ok = (), Error = ()>>();
   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ associated type `Item` must be specified

@@ -57,7 +57,7 @@ mod private_try_future {

/// A convenience for futures that return `Result` values that includes
/// a variety of adapters tailored to such futures.
pub trait TryFuture: private_try_future::Sealed {
pub trait TryFuture: Future + private_try_future::Sealed {
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Added for consistency with TryStream.

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I'm really into this! Similar to Iterator::size_hint and poll_read_vectored this seems like a method that's really useful to significantly help speed up certain code paths!

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cramertj commented Sep 3, 2019

Nice! Seems like a good easy add.

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Consider adding size_hint to Stream
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