fn inspect<F>(self, f: F) -> Inspect<Self, F>
    where
        F: FnMut(&Self::Item),
        Self: Sized,
    {
        assert_stream::<Self::Item, _>(Inspect::new(self, f))
    }
Do something with each item of this stream, afterwards passing it on.

This is similar to the `Iterator::inspect` method in the standard
library where it allows easily inspecting each value as it passes
through the stream, for example to debug what's going on.
futures-util/src/stream/stream/mod.rs