src/librustc_error_codes/error_codes/E0751.md

   1 There are both a positive and negative trait implementation for the same type.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0751
   6 trait MyTrait {}
   7 impl MyTrait for i32 { }
   8 impl !MyTrait for i32 { } // error!
   9 ```
  10
  11 Negative implementations are a promise that the trait will never be implemented
  12 for the given types. Therefore, both cannot exists at the same time.