For example, I've been doing a lot of Rust coding.

The code in question looks like:

    iter.next().ok_or(ErrorKind::NotEnoughArguments.into())?.parse().chain_err(|| "cannot parse argument")?

the compiler responds with cannot infer type information for `_`

the solution is of course to do

   iter.next().ok_or::<Error>(ErrorKind::NotEnoughArguments.into())?.parse().chain_err(|| "cannot parse argument")?

then the type inference is decidable

in a dynamic language, you wouldn't have to worry about this; in fact, you wouldn't need to call .into() either - there's just less typing and compiler errors