%w error verb
The %w directive is a Go formatting directive that wraps an error operand as the underlying cause of a formatted error.
100 Go Mistakes and How to Avoid Them
The %w directive is a Go fmt formatting directive that records an operand as the underlying error of a returned formatted error.
- How it is used
- Adds context or classification while preserving an underlying error for callers and later error handling.
- How deep it goes
- Explains wrapping, contrasts %w with %v, and traces why errors.As replaces direct type checks after refactoring.
- Examples
- Uses bar failure context, permission errors, transient database failures, and HTTP 400-versus-503 responses.
- What you can do after
- Diagnose/debug with it by preserving causes, selecting %w or %v, and checking wrapped errors accurately.
Read how 100 Go Mistakes and How to Avoid Them explains %w error verb →
Go by Example
The %w error verb is a Go formatting directive that records an operand as the wrapped cause of a returned error.
- How it is used
- Uses %w in custom command-line flag parsing to add context while preserving underlying parse errors.
- How deep it goes
- Explains wrapping and errors.Is through a worked parser example, without descending into error implementation internals.
- Examples
- Demonstrates contextual errors from a custom flag parser when strconv.Atoi rejects a flag value.
- What you can do after
- Diagnose errors with errors.Is while retaining informative command-line parsing context.
Related concepts
- error wrappingused by · Error wrapping adds contextual information to an error while preserving access to the underlying error for later propagation or inspection.
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