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+The Unsize trait should not be implemented directly. All implementations of
+Unsize are provided automatically by the compiler.
+
+Erroneous code example:
+
+```compile_fail,E0328
+#![feature(unsize)]
+
+use std::marker::Unsize;
+
+pub struct MyType;
+
+impl<T> Unsize<T> for MyType {}
+```
+
+If you are defining your own smart pointer type and would like to enable
+conversion from a sized to an unsized type with the
+[DST coercion system][RFC 982], use [`CoerceUnsized`] instead.
+
+```
+#![feature(coerce_unsized)]
+
+use std::ops::CoerceUnsized;
+
+pub struct MyType<T: ?Sized> {
+    field_with_unsized_type: T,
+}
+
+impl<T, U> CoerceUnsized<MyType<U>> for MyType<T>
+    where T: CoerceUnsized<U> {}
+```
+
+[RFC 982]: https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md
+[`CoerceUnsized`]: https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html