std::raw::Repr is not safe to implement

[brson]

Here's the definition

/// This trait is meant to map equivalences between raw structs and their
/// corresponding rust values.
pub trait Repr<T> {
    /// This function "unwraps" a rust value (without consuming it) into its raw
    /// struct representation. This can be used to read/write different values
    /// for the struct. This is a safe method because by default it does not
    /// enable write-access to the fields of the return value in safe code.
    #[inline]
    fn repr(&self) -> T { unsafe { mem::transmute_copy(&self) } }
}

Implementing is done like so:

impl<T> Repr<Slice<T>> for [T] {}

A safe implementation invokes a transmute between arbitrary types. Perhaps Repr is more appropriately an unsafe trait?

[Gankra]

Agreed. Unsafe trait is the way to go.