E3012

Record pattern and map pattern cannot be mixed. The key in map pattern must be a literal, while the key in record pattern must be the field name.

Erroneous example

struct S {
  value : Int
}

pub fn S::op_get(self : S, index : String) -> Int? {
  if index == "value" {
    return Some(self.value)
  }
  return None
}

fn main {
  let s : S = { value: 42 }
  match s {
    { "value": value, value } => println("Value is: \{value}") // Error: Record pattern and map pattern cannot be mixed.
    _ => println("No value")
  }
}

Suggestion

Remove either the map pattern part or the record pattern part from the pattern.

fn main {
  let s : S = { value: 42 }
  match s {
    { "value": value } => println("Value is: \{value}")
    _ => println("No value")
  }
}

Or,

fn main {
  let s : S = { value: 42 }
  match s {
    { value } => println("Value is: \{value}")
  }
}