Try_v2

Provides a derive macro for Try & optionally Try_ConvertResult for interconversion with std::result::Result and Try_Iterator for iterating over IntoIterator and collecting from FromIterator analogous to how Result & Option do this. See (try_trait_v2) for more details of the underlying trait.

Requires

• nightly
• #![feature(never_type)]
• #![feature(try_trait_v2)]
• #![feature(try_trait_v2_residual)]
• optionally: #![feature(iterator_try_collect)] (if using Try_Iterator)

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 full documentation for specifics on the generated code.

Example Usage

#![feature(never_type)]
#![feature(try_trait_v2)]
#![feature(try_trait_v2_residual)]
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));

Stability & MSRV

Given that this crate exposes an experimental API from std it makes use of experimental features which require a nightly toolchain.

In order to use this crate you must enable the features which it exposes:

🔬 Required Experimental Features

• #![feature(never_type)]
• #![feature(try_trait_v2)]
• #![feature(try_trait_v2_residual)]
• optionally: #![feature(iterator_try_collect)] (if using Try_Iterator)

This crate makes use of the following experimental features in addition to those which it directly supports:

🔬 Additional Experimental Features

• #![feature(if_let_guard)] (stable since 1.95.0)
• #![feature(let_chains)] (stable since 1.88.0 on 2024 only)

This list includes any unstable features used by direct & transitive dependencies (currently, none).

You do not need to enable these in your own code, the list is for information only.

Stability guarantees

We run automated tests every month to ensure no fundamental changes affect this crate and test every PR against the current nightly, as well as the current equivalent beta & stable. If you find an issue before we do, please raise an issue on github.

MSRV

For those of you working with a pinned nightly (etc.) this crate supports every version of edition 2024 (rust 1.85.1 onwards, released as stable on 2025-03-18). We use autocfg to seamlessly handle features which have been stabilised since then.

Currently untested (may work, may not ...)

• where clauses
• storing Fns in variants