Dart，为什么我的 class 在我实现 class 时没有错误，但没有覆盖每个字段，而是从 Mockito 扩展 Mock？

Question

I'm in Dart.

Why my class has no error when I implements a class without override every field, But extends Mock from Mockito?

For example,

class Base {
  void a() {}
  void b() {}
}

// NO ERROR
class ConcreteA implements Base {

  @override
  void a() {}

  @override
  void b() {}

}

// ERROR: Didn't override every field.
class ConcreteB implements Base {

  @override
  void a() {}

}

// NO ERROR
class ConcreteC extends Mock implements Base {

  @override
  void a() {}

}

How could Mockito implement this?

Answer 1

The Mock class implements Base 'magically' here because of the Mock overrides the noSuchMethod method .

  dynamic noSuchMethod(Invocation invocation, [Object /*?*/ returnValue]) {
   // noSuchMethod is that 'magic' that allows us to ignore implementing fields
   // and methods and instead define them later at compile-time per instance.
   // See "Emulating Functions and Interactions" on dartlang.org: goo.gl/r3IQUH

The methods from Base are actually implemented by Mock at compile time.

Thus, since ConcreteC is a subclass of Mock, no error should be shown.