Panic

As with Error in Dart Core, Panic represents a state that should never happen and thus should never be caught. Rust vs Dart Error handling terminology:

Result x = Err(1);
if (x.isErr()) {
  return x.unwrap(); // this will throw a Panic (should be "unwrapErr()")
}

panic can also be called directly with

throw Panic("Panic message here.");
// or 
panic("Panic message here.");

rust_core was designed with safety in mind. The only time rust_core will ever throw is if you unwrap incorrectly (as above), in this case a Panic's can be thrown. But the good news is you can usually avoid using these methods. See How to Never Unwrap Incorrectly section to avoid ever using unwrap.

Unreachable

Unreachable is shorthand for a Panic where the compiler can’t determine that some code is unreachable.

throw Unreachable();
// or
unreachable();