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withoutboats
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Der Fehler

Documentation

Der Fehler is a library to add support for "throwing functions" to Rust through procedural macros. Functions marked with the

throws
attribute return
Result
, but the "Ok" path is used by default and you don't need to wrap ok return values in
Ok
. To throw errors, use
?
or the
throws
macro.

Der Fehler provides these items:

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, it uses the default error type for this crate.

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:

#[throws(i32)]
fn foo(x: bool) -> i32 {
    if x {
        0
    } else {
        throw!(1);
    }
}

fn bar(x: bool) -> Result { if x { Ok(0) } else { Err(1) } }

In functions that return
Option

The attribute can be used to make a function that returns an Option using the

as Option
syntax, demonstrated below:
// This function returns `Option`
#[throws(as Option)]
fn foo(x: bool) -> i32 {
    if x {
        return 0;
    } else {
        throw!();
    }
}

The
throw!
macro

throw!
is a macro which is equivalent to the
Err($e)?
pattern. It takes an error type and "throws" it.

One important aspect of the

throw!
macro is that it allows you to return errors inside of functions marked with
throws
. You cannot just
return
errors from these functions, you need to use this macro.

TODO

  • Make throws work on closures and async blocks (attributes are not allowed on expressions on stable)
  • Make throws work on Try types other than Result and Option (TRy is not on stable).

License

Licensed under either of

  • Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
  • MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

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