Why do I get an error when pattern matching a struct-like enum variant with fields?

Question

I can\'t get rid of an error on this code:

#[derive(PartialEq, Copy, Clone)]
pub enum OperationMode {
    ECB,
    CBC { iv: [u8; 16] },
}

pub struct AES {
         


        

Answer 1

Enum variants have three possible syntaxes:

• unit

  enum A { One }
  

• tuple

  enum B { Two(u8, bool) }
  

• struct

  enum C { Three { a: f64, b: String } }
  

You have to use the same syntax when pattern matching as the syntax the variant was defined as:

• unit

  match something {
      A::One => { /* Do something */ }
  }
  

• tuple

  match something {
      B::Two(x, y) => { /* Do something */ }
  }
  

• struct

  match something {
      C::Three { a: another_name, b } => { /* Do something */ }
  }
  

Beyond that, you can use various patterns that allow ignoring a value, such as _ or ... In this case, you need curly braces and the .. catch-all:

OperationMode::CBC { .. } => { /* Do something */ }

See also:

• Ignoring Values in a Pattern in The Rust Programming Language
• Appendix B: Operators and Symbols in The Rust Programming Language
• How to match struct fields in Rust?