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In <boost/outcome/experimental>, there ships an Outcome-based simulation of the proposed P1095 Zero overhead deterministic failure specific implementation of P0709 Zero overhead exceptions: Throwing values, aka “Herbceptions”. This library-only implementation lets you use a close simulacrum of potential future C++ lightweight exceptions today in any C++ 14 compiler which Outcome supports.


It is stressed, in the strongest possible terms, that any item inside <boost/outcome/experimental> is subject to unannounced breaking change based on WG21 standards committee feedback. That said, the chances are high that most of those breaking changes will be to naming rather than to fundamental semantics, so you can upgrade with a bit of find and replace. There are quite a few large code bases out there already using this experimental support in anger, we know it works well at scale and it’s a good bit superior to std::error_code et al on every measure.

P1095’s support library has a reference implementation at You will find terse documentation there, and an API reference. This library is wholly incorporated into Outcome in the <boost/outcome/experimental/status-code> directory, with bindings into Outcome provided in the following headers:

These headers import the entire contents of the BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE namespace into the BOOST_OUTCOME_V2_NAMESPACE::experimental namespace. You can thus address everything in BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE via BOOST_OUTCOME_V2_NAMESPACE::experimental.

As P1095 also proposes C language support for lightweight C++ exceptions, experimental Outcome also has a macro-based C interface that enables C code to work with the C-compatible subset of status_result<T, E>:

Last revised: January 26, 2019 at 21:01:46 UTC

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