Remove uses of transmute

[nox]

Most uses of transmute are useless and security hazards, they should be replaced by something less magical. For examples the various transmute calls in from_u8 methods can be replaced entirely by safe code.

[nwin]

Do we have a good replacement of FromPrimitive by now? That is the sole reason that code exists in the first place.

Must uses of transmute are unfortunately not unnessesary here but caused by limitations of rustc. Replacing them would make the code much slower and harder to read.

[nox]

The good replacement is to make match arms and let the optimiser get rid of it. It also help readability, contrary to what you just stated.

[nwin]

I was referring to most uses of transmute which is not in from_u8.

[nox]

They all hurt readability.

[nwin]

Which is simply not true. If you find a replacement which doesn't involve wild boxing I'm happy to make that change. As you can read from the comments I tried hard to get rid of them.

[est31]

Do we have a good replacement of FromPrimitive by now

There are a couple of crates for that:

• https://crates.io/crates/enum_primitive
• https://crates.io/crates/derive-try-from-primitive

[Shnatsel]

Transmutes for from_u8 have been removed. Only two instances of the following lifetime-related transmutes remain:

// This transmute just casts the lifetime away. Since Rust only
// has SESE regions, this early return cannot be worked out and
// such that the borrow region of self includes the whole block.
// The explixit lifetimes in the function signature ensure that
// this is safe.
// ### NOTE
// To check that everything is sound, return the result without
// the match (e.g. `return Ok(try!(self.next_state(buf)))`). If
// it compiles the returned lifetime is correct.
unsafe {
    mem::transmute::<Decoded, Decoded>(result)
}

I wonder if the upcoming non-lexical lifetimes would help with that?