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`Result<T, dyn Error>` from Rust (since I'm not a Haskeler) is a result that can contain any error. Which is exactly what unchecked exceptions are. Rust develo

• chriswarbo 6y ago
  > Rust developers can fluently switch and convert between conrete `Result<T, SomeErrorEnumeration>` and `Result<T, dyn Error>` That's something different, since both cases tell you that errors might occur. In Java we can do the following: public int concreteChecked() throws FileNotFound { if (bar) throw new FileNotFound(); return 42; } public int polymorphicChecked() throws Exception { if (bar) throw new FileNotFound(); return 42; } public Either<FileNotFound, int> concreteEither() { return bar? new Left(new FileNotFound()) : new Right(42); } public Either<Exception, int> polymorphicEither() { return bar? new Left(new FileNotFound()) : new Right(42); } public int unchecked() { if (bar) throw new RuntimeException(new FileNotFound()); return 42; } I think your 'Result' examples are like the third and fourth examples above: using a sum type, differing by whether the error is more/less specific. The first and second use checked exceptions, again differing in whether the error is more/less specific. Importantly: these will refuse to compile if we don't have 'throws ...' in their signature. The last example uses an unchecked exception: if we throw 'RuntimeException' (or a subclass), we don't need to put 'throws ...' in the signature, and hence the compiler won't keep tell us to put 'catch' block anywhere.
  • dpc_pw 6y ago
    In Rust you can do `Result<T, dyn SomeErrorInterface>` as well, which makes it able to express everything exactly like Java can. It's just Rust community generally doesn't bother with the taxonomies of errors. You either get a concrete list, or "any error".