Question

_distance变量是否可能是最终变量，但仍然在Dart对象的构造函数中保留类型签名？

Function _distance;

ExampleConstuctor(num distanceFunction(T a, T b)) {
  _distance = distanceFunction;
}

Answer 1

在1.24.0中，我们正在引入一种新语法来完成这项工作：

https://github.com/dart-lang/sdk/blob/master/CHANGELOG.md#language-1

typedef F = void Function();  // F is the name for a `void` callback.
int Function(int) f;  // A field `f` that contains an int->int function.

class A<T> {
  // The parameter `callback` is a function that takes a `T` and returns
  // `void`.
  void forEach(void Function(T) callback);
}

// The new function type supports generic arguments.
typedef Invoker = T Function<T>(T Function() callback);

在此之前，您还可以使用package:func中声明的各种typedef：

https://pub.dartlang.org/packages/func

Answer 2

您可以使用typedef：

typedef num DistanceFunction<T>(T a, T b);

class ExampleConstructor<T> {
  final DistanceFunction<T> _distance;

  ExampleConstructor(this._distance);
}

Answer 3

除上述答案外，我还发现这有效：

class ExampleConstructor<T> {
  final Function _distance;

  ExampleConstructor(num this._distance(T a, T b)) 
}

飞镖最终功能

3 个答案: