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.