Errors.As
errors.As is a Go standard-library function that searches an error chain for a value assignable to a specified type and stores the result.
Learn Go with Pocket-Sized Projects
errors.As is a Go function that finds an error assignable to a target type and stores it through the supplied target pointer.
- How it is used
- Classifies returned errors so HTTP clients can detect timeouts and gRPC endpoints can select API status codes.
- How deep it goes
- Explains the Boolean result, target population, and pointer-to-pointer requirement, then applies type-specific methods and API mapping.
- Examples
- Demonstrates HTTP timeout detection and InvalidInputError translation in a gRPC CreateHabit endpoint.
- What you can do after
- Diagnose typed failures and route them to timeout handling or precise gRPC status responses.
Read how Learn Go with Pocket-Sized Projects explains errors.As →
Go by Example
errors.As is a Go standard-library function that searches an error chain for a value assignable to a specified error type and stores the result.
- How it is used
- Translates inspected driver and custom errors into meaningful application-level outcomes without exposing internal details.
- How deep it goes
- Explains chain extraction, target typing, pointer receivers, error-code inspection, and typed-nil custom-error pitfalls.
- Examples
- Uses SQLite primary-key code 1555, Shorten duplicate keys, ErrConflict, and a custom NotFoundError carrying an ID.
- What you can do after
- Apply it to extract concrete errors, inspect their details, and map them to stable application errors.
100 Go Mistakes and How to Avoid Them
errors.As is a Go standard-library function that recursively examines an error chain for an error assignable to a specified target type.
- How it is used
- Classifies wrapped errors so handlers can choose responses such as service-unavailable or bad-request status codes.
- How deep it goes
- Traces wrapping, recursive unwrapping, type matching, and the runtime panic caused by a non-pointer target.
- Examples
- Demonstrates transientError, database failure propagation, and HTTP response handling.
- What you can do after
- Diagnose/debug wrapped errors and route them according to their underlying type.
Read how 100 Go Mistakes and How to Avoid Them explains errors.As →
Go in Action, Second Edition
errors.As is a Go standard-library function that finds an error in an error chain assignable to a specified type and stores it in a destination value.
- How it is used
- Uses errors.As to recover typed error details when ordinary error messages or values do not provide enough information for handling.
- How deep it goes
- Explains error-chain matching, destination pointers, boolean results, and deferred handling, but does not detail the implementation internals.
- Examples
- Demonstrates recovering bulkGetError from BulkGet and using its missing keys to insert temporary store values.
- What you can do after
- Diagnose errors with errors.As by retrieving a matching typed value and acting on its additional data.
Related concepts
- errorsimplemented by · errors is Go’s standard-library package for creating, wrapping, comparing, and inspecting error values.
- error chainuses · An error chain is a linked sequence of wrapped Go error values that preserves an underlying cause and added context.
- error handlingused by · Error handling is the practice of detecting, representing, propagating, reporting, and responding to errors or failures during software operation.
- pointeruses · A pointer is a value that refers to a memory location or another object, enabling indirect access to it.
- failureuses · A failure is an unsuccessful outcome or condition in which an operation, process, or system does not achieve an expected result.
- interfaceuses · A software interface is a contract or boundary that specifies the operations, properties, or capabilities through which types or components interact, without requiring a particular implementation.
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