Sentinel error
A sentinel error is a predefined error value with stable identity that represents a specific failure condition for programmatic comparison.
Learn Go with Pocket-Sized Projects
A sentinel error is a predefined error value or type that callers can compare or check to identify a specific domain condition.
- How it is used
- Exposes domain conditions that other packages can recognize without coupling consumers to implementation-specific errors.
- How deep it goes
- Defines the custom type, return sites, wrapping, and tests, but stops short of broader error-taxonomy design.
- Examples
- Uses empty-corpus detection, ReadCorpus, ErrCorpusIsEmpty, ErrCallingServer, and table-driven tests.
- What you can do after
- Build it from scratch and apply it via errors.Is to expose stable, package-specific failure conditions.
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Go in Action, Second Edition
A sentinel error is a predefined error value identified by comparison so callers can make programmatic decisions about a failure condition.
- How it is used
- Uses stable package-level values to let callers branch on common failure conditions.
- How deep it goes
- Explains declaration, return, errors.Is checks, wrapping, and the point where custom error types carry extra data.
- Examples
- Uses KVStore operations, ErrConflict, ErrNotExist, io.EOF, ForcePut, and bulk retrieval of missing keys.
- What you can do after
- Apply it via errors.Is to recognize known conditions, including conditions preserved inside wrapped errors.
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100 Go Mistakes and How to Avoid Them
An error sentinel is a predefined error value representing a known condition that callers can compare against.
- How it is used
- Guides expected-error design and reliable caller checks in Go error handling.
- How deep it goes
- Explains declaration, expected-versus-unexpected classification, direct comparison, and wrapped-error checks.
- Examples
- Uses ErrFoo, sql.ErrNoRows, io.EOF, query handling, and direct versus wrapped comparisons.
- What you can do after
- Diagnose/debug with it by distinguishing expected conditions and checking sentinels correctly through wrapped errors.
Read how 100 Go Mistakes and How to Avoid Them explains sentinel error →
Related concepts
- errors.Isused by · errors.Is is a Go standard-library function that reports whether an error or any error in its wrapping chain matches a target error.
- error variableequivalent to · An error variable is a package-scoped Go variable whose value identifies a particular error condition and can be compared or returned by Go code.
- error valuekind of · An error value is a value representing a failure condition that an operation or function can return.
- failurecontrasts with · A failure is an unsuccessful outcome or condition in which an operation, process, or system does not achieve an expected result.
- error handlinguses · Error handling is the practice of detecting, representing, propagating, reporting, and responding to errors or failures during software operation.
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