Idiomatic alternative to reflection in Rust

I am trying to select a digest algorithm (from rust-crypto) based on a configuration string. In Python or JavaScript, say, I'd probably use reflection to get at this:

getattr(Digest, myAlgorithm)

...but from what I've been able to Google, this isn't best practice in a language such as Rust (plus I've found no details on how it could be done). My initial thought was to use a pattern match:

let mut digest = match myAlgorithm {
  "sha256" => Sha256::new(),
  ...
};

However, this doesn't work because, while all the branches of the match implement the same trait, they're ultimately different types. Moreover, presuming there were a way around this, it's a lot of hassle to manually enumerate all these options in the code.

What's the right way to do this in Rust?