crypto-mac v0.9

[newpavlov]

• Add FromBlockCipher trait and respective NewMac blanket implementation
• Bump blobby to v0.3
• Remove impl_write! macro, since it's useless for generic types

I couldn't make code generic over From<BlockCipher> trait due to the "unconstrained type parameter" error, so I had to introduce a new non-polymorphic trait instead. Any ideas how this problem can be worked around?

[tarcieri]

I couldn't make code generic over From trait due to the "unconstrained type parameter" error, so I had to introduce a new non-polymorphic trait instead. Any ideas how this problem can be worked around?

What's the concrete error? Do you have a full example?

[newpavlov]

I've tried the following code:

impl<T, C> NewMac for T
where
    T: From<C>,
    C: BlockCipher + NewBlockCipher,
{
    type KeySize = C::KeySize;

    fn new(key: &Key<Self>) -> Self {
        C::new(key).into()
    }

    fn new_varkey(key: &[u8]) -> Result<Self, InvalidKeyLength> {
        C::new_varkey(key).map_err(|_| InvalidKeyLength)?.into()
    }
}

And I get this compilation error:

error[E0207]: the type parameter `C` is not constrained by the impl trait, self
type, or predicates
   --> crypto-mac/src/lib.rs:124:9
    |
124 | impl<T, C> NewMac for T
    |         ^ unconstrained type parameter

error: aborting due to previous error

Which in hindsight should've been expected. Right now I have no idea how to properly structure code and if it's even possible in principle.

[tarcieri]

@newpavlov aah yeah, that looks similar to what I was running into with signature. I ended up solving it with custom derive.

[newpavlov]

So what do you think? Should we go ahead with the current code for the time being?

[tarcieri]

Seems fine to me