StatusOr

StatusOr is a template concept used in several C++ libraries to represent either a value of a specified type or an error status. It is most commonly associated with Abseil’s absl::StatusOr<T>, but the idea appears in various forms across frameworks that implement a non-exception error handling strategy. A StatusOr<T> encapsulates a successful result alongside a meaningfully typed error state, enabling functions to propagate failure without throwing exceptions.

In typical implementations, a StatusOr<T> internally stores either a value of type T or an error status object (often containing an error code and message). The interface usually provides a way to test for success, such as a boolean conversion or an ok() method, and separate accessors for the value and for the status. Accessing a value when the status indicates failure is considered a programming error in many designs. Because of the separation between value and status, StatusOr encourages explicit handling of failure paths at call sites.

Common usage patterns involve functions that return StatusOr<T> to indicate possible failure. Callers check the status first and then retrieve the value if successful, or propagate or log the error otherwise. This approach aims to combine the clarity of explicit error handling with the efficiency of avoiding exceptions.

Related concepts include the general idea of an expected or result type, optional wrappers, and the broader category of status-based error handling in APIs. StatusOr is valued for making error propagation explicit while preserving the ability to return rich error information.

---