E0053

Warning name: unused_trait_bound

Unused trait bound.

The polymorphic function or method has a trait bound that is not used. This could be a potential bug that you have forgotten to apply the methods from the trait.

Erroneous example

///|
trait Any {}

///|
pub fn[T : Any] check(_ : T) -> Unit {
  println("Hello")
}

///|
pub fn[T : Compare] shortlex(a : Array[T], b : Array[T]) -> Int {
  Int::compare(a.length(), b.length())
}

Suggestion

There are multiple ways to fix this warning:

• If this trait bound is unnecessary, you can remove it

  
  ///|
  pub fn[T] check(_ : T) -> Unit {
    println("Hello")
  }
  
  

• You can cast the variable to a trait object

  
  ///|
  pub fn[T : Any] check_any(t : T) -> Unit {
    let _ = t as &Any
    println("Hello")
  }
  
  

• You can use the methods defined in the Trait

  
  ///|
  pub fn[T : Compare] shortlex(a : Array[T], b : Array[T]) -> Int {
    match Int::compare(a.length(), b.length()) {
      _..<0 => -1
      1..<_ => 1
      0 =>
        for i = 0; i < a.length(); i = i + 1 {
          match T::compare(a[i], b[i]) {
            _..<0 => return -1
            1..<_ => return 1
            0 => ()
          }
        } nobreak {
          return 0
        }
    }
  }