使用“类型”的Dart类型检查 [英] Dart type check using "Type"

问题描述

如何使用Child类实例检查Super类的类型？我有以下例子，不想使用dart-mirror。

How to check type of Super class with Child class instance? I have below example and don't want to use dart-mirrors.

class SomeClass{

}

class SomeOtherClass extends SomeClass{

}
void main() {
  var s1 = new SomeOtherClass();
  someMethod(SomeClass, s1);
}

void someMethod(Type t, dynamic instance){
  print(instance.runtimeType == t);
  //print(instance.runtimeType is t); Does not work!
}

推荐答案

更新

只是今天，包可反映已发布，允许做这类似于镜像，但是变换器生成代码，以避免在生产中使用镜像。

Update

Just today the package reflectable was released which allows to do this like with mirrors, but a transformer generates code instead to avoid using mirrors in production.

import 'package:reflectable/reflectable.dart';

// Annotate with this class to enable reflection.
class Reflector extends Reflectable {
  const Reflector()
  : super(typeCapability); // Request the capability to invoke methods.
}

const reflector = const Reflector();

@reflector
class SomeClass{

}

@reflector
class SomeOtherClass extends SomeClass{

}

void someMethod(Type t, dynamic instance){
  InstanceMirror instanceMirror = reflector.reflect(instance);
  print(instanceMirror.type.isSubclassOf(reflector.reflectType(t)));
}

void main() {
  var s1 = new SomeOtherClass();
  someMethod(SomeClass, s1);
}

原始

在实施 https://github.com/gbracha/metaclasses 时，可能会直接受到支持。

Original

It might be directly supported when https://github.com/gbracha/metaclasses is implemented.

目前可以使用此解决方法：

Currently this workaround can be used:

class IsInstanceOf<E> {
  bool check(t) => t is E;
}

void someMethod(Type t, dynamic instance){
  print( new IsInstanceOf<t>().check(instance));
  //print(instance.runtimeType is t); Does not work!
}

这样运行正常，返回正确的结果，但分析仪显示警告， code> t 不能用作类型。

This runs fine and returns the correct result but the analyzer shows a warning because t can't be used as a type.

如果换行 SomeClass 在一个泛型类中它工作没有警告

If you wrap SomeClass in a generic class it works without a warning

class SomeClass{

}

class SomeOtherClass extends SomeClass{

}

void main() {
  var s1 = new SomeOtherClass();
  someMethod(new IsInstanceOf<SomeClass>(), s1);
}

void someMethod(IsInstanceOf t, dynamic instance){
  print(t.check(instance));
  //print(instance.runtimeType is t); Does not work!
}

class IsInstanceOf<E> {
  bool check(instance) => instance is E;
}

请尝试 DartPad

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