Error code E0023
A pattern attempted to extract an incorrect number of fields from a variant.
Erroneous code example:
#![allow(unused)] fn main() { enum Fruit { Apple(String, String), Pear(u32), } let x = Fruit::Apple(String::new(), String::new()); match x { Fruit::Apple(a) => {}, // error! _ => {} } }
A pattern used to match against an enum variant must provide a sub-pattern for each field of the enum variant.
Here the Apple
variant has two fields, and should be matched against like so:
#![allow(unused)] fn main() { enum Fruit { Apple(String, String), Pear(u32), } let x = Fruit::Apple(String::new(), String::new()); // Correct. match x { Fruit::Apple(a, b) => {}, _ => {} } }
Matching with the wrong number of fields has no sensible interpretation:
#![allow(unused)] fn main() { enum Fruit { Apple(String, String), Pear(u32), } let x = Fruit::Apple(String::new(), String::new()); // Incorrect. match x { Fruit::Apple(a) => {}, Fruit::Apple(a, b, c) => {}, } }
Check how many fields the enum was declared with and ensure that your pattern uses the same number.