E4100

The type is not a trait.

This error occurs when you try to use the typealias syntax to define a alias for a type and use it as a trait. As it is impossible to use a type as a trait, this error might hint at a typo in your code.

错误示例

type Original Int

typealias Alias = Original

trait Trait: Alias {
  //         ^~~~~
  // Error: The type Alias is not a trait
}

建议

If there is a typo, the use a correct trait or alias of trait at where the error occurs.

trait Original {
  to_int(Self) -> Int
}

typealias Alias = Original

trait Trait: Alias {
  to_int(Self) -> Int
}

We recommend using traitalias for defining aliases for traits, as this will detect errors like this earlier.