Der Fehler
Der Fehler is a small but very opinionated Rust error handling library.
In many ways, der Fehler is a successor to failure. However, unlike failure,
der Fehler is built around the standard library's Error
trait, which has
adopted the necessary improvements that the Fail
trait had provided thanks to
RFC 2504.
Der Fehler provocatively and unapologetically uses the terminology of exceptions.
Der Fehler provides these items:
The Exception
type
Exception is a polymorphic error type, essentially a trait object. It is
similar to the failure::Error
type, but for the Error
trait in std. There
are a few key improvements:
- Like
failure::Error
is possible to construct an ad hoc error from any type that implementsDebug
andDisplay
(such as a string). Unlikefailure::Error
, it can be properly downcast to that type. - Unlike
failure::Error
,Exception
is guaranteed to be the size of a single narrow pointer (failure::Error
is the size of a wide pointer).
Otherwise, it is roughly the same type: an Error trait object that guarantees the presence of a backtrace.
The throw!
macro
throw!
is a macro which is equivalent to the Err($e)?
pattern. It takes an
error type and "throws" it.
The #[throws]
attribute
The throws attribute modifies a function or method to make it return a
Result
. It takes an optional typename as an argument to the attribute which
will be the error type of this function; if no typename is supplied, the error
type is Exception
.
Within the function body, return
s (including the implicit final return) are
automatically "Ok-wrapped." To raise errors, use ?
or the throws!
macro.
For example, these two functions are equivalent:
The error!
macro
This macro constructs an ad hoc error from format strings, similar to the
format!
macro.
The Context
trait
This crate also defines a Context
trait for the Result
type, which
contains a context
method for injecting context around an error.
TODO
- Possibly add a Display derive
- Make throws work on closures and async blocks (attributes are not allowed on expressions on stable)