dart 'with' mixin classes

main.dart

abstract class SayI{
  String say();
  String get str;
}

abstract class SayMixinA implements SayI{
  String get str;

  String say() {
    print('SayMixinA:say:print runtimeType: $runtimeType str: $str');
    return 'SayMixinA:say:string runtimeType: $runtimeType str: $str';
  }
}

abstract class SayMixinB implements SayI{
  String get str;

  String say() {
    print('SayMixinB:say:print runtimeType: $runtimeType str: $str');
    return 'SayMixinB:say:string runtimeType: $runtimeType str: $str';
  }
}

class SayImplA extends SayI with SayMixinA, SayMixinB{
  final String str = 'str-SayImplA';
  SayImplA(){
    print('SayImplA:constructor...');
    print('SayImplA:constructor return: ${say()}');
  }
}

class SayImplB extends SayI with SayMixinB, SayMixinA{
  final String str = 'str-SayImplB';
  SayImplB(){
    print('SayImplB:constructor...');
    print('SayImplB:constructor return: ${say()}');
  }
}

void main() {

  print(' ====================== ');
  final SayI sayImplA = SayImplA();

  print('\n\n\n\n ====================== ');
  final SayI sayImplB = SayImplB();
}

result

 ======================
SayImplA:constructor...
SayMixinB:say:print runtimeType: SayImplA str: str-SayImplA
SayImplA:constructor return: SayMixinB:say:string runtimeType: SayImplA str: str-SayImplA




 ======================
SayImplB:constructor...
SayMixinA:say:print runtimeType: SayImplB str: str-SayImplB
SayImplB:constructor return: SayMixinA:say:string runtimeType: SayImplB str: str-SayImplB

dart --version: Dart VM version: 2.1.0-dev.4.0 (Fri Sep 7 16:44:38 2018 +0200) on "macos_x64"

order of mixin class matters, it's executed from backward. and once it found the requested method, it won't further execute the corresponding method that's implemented by other mixin class
(but is this intended behavior? I for one would expect that all the mixins will be executed, though the results/returned value being overridden is kinda as expected)

run it in dart pad yourself