E0063
Rust Compiler Error
Severity: MinorWhat Does This Error Mean?
Rust E0063 means you initialised a struct without providing values for all of its fields. The error names the missing fields. Either provide values for each field, use struct update syntax (..default), or derive the Default trait.
Affected Models
- Rust (all stable versions)
Common Causes
- Struct has fields that were not provided in the initializer
- A new field was added to the struct and existing initializers were not updated
- Using struct literal syntax without knowing all required fields
- Copy-paste of an initializer from an older version of the struct
- Forgot to use struct update syntax when doing a partial initializer
How to Fix It
-
Add values for each field listed in the error message.
The E0063 message names every missing field. Go to the struct definition to see the expected types and provide appropriate values for each.
-
Use struct update syntax to fill remaining fields from a default value.
Example: let s = MyStruct { name: String::from(hello), ..MyStruct::default() }; This fills unspecified fields with default values — the struct must implement the Default trait.
-
Derive the Default trait on the struct if most fields have sensible zero-values.
Add #[derive(Default)] above the struct definition. Then use MyStruct { specific_field: value, ..Default::default() } to set only the fields you care about.
Frequently Asked Questions
Does Rust require all struct fields to be initialised?
Yes — Rust requires all struct fields to be explicitly initialised when using struct literal syntax. This guarantees no field is ever in an uninitialised state, which is a core memory safety guarantee.
Can I add a new field to a Rust struct without breaking all existing initializers?
Not easily with struct literal syntax. To allow partial initialisation, derive Default and use struct update syntax in existing code. Alternatively, use a builder pattern — this lets you add optional fields without breaking callers.