How to read (std::io::Read) from a Vec or Slice?

While vectors don’t support std::io::Read, slices do.

There is some confusion here caused by Rust being able to coerce a Vec into a slice in some situations but not others.

In this case, an explicit coercion to a slice is needed because at the stage coercions are applied, the compiler doesn’t know that Vec<u8> doesn’t implement Read.

The code in the question will work when the vector is coerced into a slice using one of the following methods:

• read_4_bytes(&*vec_as_file)
• read_4_bytes(&vec_as_file[..])
• read_4_bytes(vec_as_file.as_slice()).

Note:

• When asking the question initially, I was taking &Read instead of Read. This made passing a reference to a slice fail, unless I’d passed in &&*vec_as_file which I didn’t think to do.
• Recent versions of rust you can also use as_slice() to convert a Vec to a slice.
• Thanks to @arete on #rust for finding the solution!