compiler/rustc_error_codes/src/error_codes/E0283.md

   1 An implementation cannot be chosen unambiguously because of lack of information.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0283
   6 trait Generator {
   7     fn create() -> u32;
   8 }
   9
  10 struct Impl;
  11
  12 impl Generator for Impl {
  13     fn create() -> u32 { 1 }
  14 }
  15
  16 struct AnotherImpl;
  17
  18 impl Generator for AnotherImpl {
  19     fn create() -> u32 { 2 }
  20 }
  21
  22 fn main() {
  23     let cont: u32 = Generator::create();
  24     // error, impossible to choose one of Generator trait implementation
  25     // Should it be Impl or AnotherImpl, maybe something else?
  26 }
  27 ```
  28
  29 This error can be solved by adding type annotations that provide the missing
  30 information to the compiler. In this case, the solution is to use a concrete
  31 type:
  32
  33 ```
  34 trait Generator {
  35     fn create() -> u32;
  36 }
  37
  38 struct AnotherImpl;
  39
  40 impl Generator for AnotherImpl {
  41     fn create() -> u32 { 2 }
  42 }
  43
  44 fn main() {
  45     let gen1 = AnotherImpl::create();
  46
  47     // if there are multiple methods with same name (different traits)
  48     let gen2 = <AnotherImpl as Generator>::create();
  49 }
  50 ```