To be clear, the only difference between Rust and C here is whether the conversion happens by default or not. Rust doesn't do the conversion by default but will let you do it if you want to, with `as`.
There are also more type-safe conversion methods that perform a more focused conversion. Eg a widening conversion from i8 -> i16 can be done with .into(), a narrowing conversion from i16 -> i8 can be done with .try_into() (which returns a Result and forces you to handle the overflow case), a signed to unsigned reinterpretation like i64 -> u64 can be done with .cast_unsigned(), and so on. Unlike `as` these have the advantage that they stop compiling if the original value changes type; eg if you refactor something and the i8 in the first example becomes an i32, the i32 -> i16 conversion is no longer a widening conversion so the `.into()` will fail to compile.
Yes that's correct, for exactly the reason that it is more likely to keep compiling and possibly not do what you intended if the original value's type changes due to refactoring. However there are still a few conversions that don't have alternatives to `as` - truncating conversions (eg i64 -> i32 that intentionally discards the upper half), int <-> float conversions (eg i64 -> f64, both truncating and checked conversions), unsized pointer casts (eg *const [MaybeUninit<u8>] -> *const [u8], `.cast()` only works for Sized target), and probably a few more.
There are also more type-safe conversion methods that perform a more focused conversion. Eg a widening conversion from i8 -> i16 can be done with .into(), a narrowing conversion from i16 -> i8 can be done with .try_into() (which returns a Result and forces you to handle the overflow case), a signed to unsigned reinterpretation like i64 -> u64 can be done with .cast_unsigned(), and so on. Unlike `as` these have the advantage that they stop compiling if the original value changes type; eg if you refactor something and the i8 in the first example becomes an i32, the i32 -> i16 conversion is no longer a widening conversion so the `.into()` will fail to compile.