+#[cfg(feature = "std")]
+pub(crate) use std::io::{self, Cursor, Read};
+#[cfg(feature = "no-std")]
+pub(crate) use core2::io::{self, Cursor, Read};
+#[cfg(feature = "no-std")]
+use alloc::{boxed::Box, vec::Vec, string::String};
+
+#[repr(C)]
+/// A dummy struct of which an instance must never exist.
+/// This corresponds to the Rust type `Infallible`, or, in unstable rust, `!`
+pub struct NotConstructable {
+ _priv_thing: core::convert::Infallible,
+}
+impl From<core::convert::Infallible> for NotConstructable {
+ fn from(_: core::convert::Infallible) -> Self { unreachable!(); }
+}