`transmute` has two restrictions I'm not sure you have added here:

[philberty]

transmute has two restrictions I'm not sure you have added here:

1. Input and output size must be identical.
2. Input and output size must be statically known before monomorphization so eg transmute::<T, U> is not allowed, but eg transmute::<PhantomData<T>, PhantomData<U>> is allowed. Note that types like [T; 0] are not considered to be of a fixed size for the purpose of this check.

Originally posted by @bjorn3 in #1194 (comment)