Why does the usage of by_ref().take() differ between the Iterator and Read traits?

Question

Here are two functions:

fn foo(iter: &mut I)
where
    I: std::iter::Iterator,
{
    let x = iter.by_ref();
    let y = x.take(         


        

Answer 1

impl<'a, I: Iterator + ?Sized> Iterator for &'a mut I is the reason why the first function compiles. It implements Iterator for all mutable references to iterators.

The Read trait has the equivalent, but, unlike Iterator, the Read trait isn't in the prelude, so you'll need to use std::io::Read to use this impl:

use std::io::Read; // remove this to get "cannot move out of borrowed content" err

fn foo(iter: &mut I)
where
    I: std::iter::Iterator,
{
    let _y = iter.take(2);
}

fn bar(iter: &mut I)
where
    I: std::io::Read,
{
    let _y = iter.take(2);
}

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