Crate try_v2 

Provides a derive macro for Try (try_trait_v2)

Also enables inter-conversion from Result<T, E> where E: Into::into(Self) and back where E: From::from<Self<!>>

Requires:

• nightly or RUSTC_BOOTSTRAP = 1
• #![feature(never_type)]
• #![feature(try_trait_v2)]

Limitations on the annotated type:

• must be an enum
• must have at least one generic type
• the first generic type must be the Output type (produced when not short circuiting)
• the output variant (does not short-circuit) must be the first variant and store the output type as the only unnamed field

See the individual documentation for Try for specifics on the generated code.

Example Usage:

#![feature(never_type)]
#![feature(try_trait_v2)]
use try_v2::{Try, Try_ConvertResult};

#[derive(Try, Try_ConvertResult)]
enum TestResult<T> {
    Ok(T),
    TestsFailed,
    OtherError(String)
}

// Basic short circuiting thanks to `#[derive(Try)]`
fn run_tests() -> TestResult<()> {
    TestResult::OtherError("oops!".to_string())?; // <- Function short-circuits here ...
    TestResult::TestsFailed?;
    TestResult::Ok(())
}

assert!(matches!(run_tests(), TestResult::OtherError(msg) if msg == "oops!"));


// Conversion from std::result::Result thanks to `#[derive(Try_ConvertResult)]`
struct TestFailure {}

impl<T> From<TestFailure> for TestResult<T> {
    fn from(err: TestFailure) -> Self {
        TestResult::TestsFailed
    }
}

fn run_more_tests() -> TestResult<()> {
    std::result::Result::Err(TestFailure{})?; // <- Function short-circuits here & converts to a TestResult...
    TestResult::Ok(())
}

assert!(matches!(run_more_tests(), TestResult::TestsFailed));

MSRV

1.85.1 if you are walking the grey-zone between stable and nightly via RUSTC_BOOTSTRAP

Currently untested (may work, may not …):

• where clauses
• storing Fns in variants

Derive Macros

Try

Derives try_trait_v2

Try_ConvertResult

Derives ?-conversion from Result<T, E> and back where suitable implementations of From/Into exist.