Lifetime problem when trying to wrap

help
#1

Hi there,

Below this is a simplified version of the code showing the problem I run into (you can just copy paste and compile it).

The code is fine until I tried wrapping the incoming stream in a BufferStream inside the NormalStream::new() function as shown below.

The compiler then complains:

error[E0310]: the parameter typeTmay not live long enough --> library-runtime/src/streams/example.rs:32:15 | 29 | impl<T> NormalStream<T> { | - help: consider adding an explicit lifetime bound...:T: 'static... 32 | stream: Box::new(BufferStream::new(stream)), | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | note: ...so that the typestreams::example::BufferStream` will meet its required lifetime bounds
--> library-runtime/src/streams/example.rs:32:15
|
32 | stream: Box::new(BufferStream::new(stream)),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

`
Making that T into a 'static lifetime feels wrong, but I am not sure how to properly fix this. I'd really like to wrap that stream (essentially adding some kind of buffer to it).

Can this be solved in a better way and if so how to do that?

Thank you for your time!

pub trait Stream<T> {
  fn next(&self) -> Option<T>;
}

pub trait StreamMark<T>: Stream<T> {
  fn mark(&self);
}

pub struct BufferStream<T> {
  stream: Box<dyn Stream<T>>,
}

impl<T> BufferStream<T> {
  pub fn new(stream: Box<dyn Stream<T>>) -> Self {
    return BufferStream { stream };
  }
}

impl<T> Stream<T> for BufferStream<T> {
  fn next(&self) -> Option<T> {
    unimplemented!()
  }
}

pub struct NormalStream<T> {
  stream: Box<dyn Stream<T>>,
}

impl<T> NormalStream<T> {
  pub fn new(stream: Box<dyn Stream<T>>) -> Self {
    return NormalStream {
      stream: Box::new(BufferStream::new(stream)), // <-- Wrapping here it's unhappy
    };
  }
}
#2

I've just solved it, so for future readers the pasting the working, note the lifetime 'a in NormalStream:

pub trait Stream<T> {
  fn next(&self) -> Option<T>;
}

pub trait StreamMark<T>: Stream<T> {
  fn mark(&self);
}

pub struct BufferStream<T> {
  stream: Box<dyn Stream<T>>,
}

impl<T> BufferStream<T> {
  pub fn new(stream: Box<dyn Stream<T>>) -> Self {
    return BufferStream { stream };
  }
}

impl<T> Stream<T> for BufferStream<T> {
  fn next(&self) -> Option<T> {
    unimplemented!()
  }
}

pub struct NormalStream<'a, T> {
  stream: Box<dyn Stream<T> + 'a>,
}

impl<'a, T: 'a> NormalStream<'a, T> {
  pub fn new(stream: Box<dyn Stream<T>>) -> Self {
    return NormalStream {
      stream: Box::new(BufferStream::new(stream)), 
    };
  }
}