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我可能会做一些错误语法或几乎所以可选的回调“不这样做”可能是有效的,但似乎这应该工作:与可选参数
class Thing {
//static dynamic noop =() { }; // fails
static dynamic noop = ([dynamic value]) { }; // works for null cases
dynamic _callback;
Thing._([dynamic callback([dynamic value])])
: this._callback = callback != null ? callback : Thing.noop;
factory Thing([dynamic callback([dynamic value])]) {
return new Thing._(callback);
}
}
当我运行这些测试时,第一一个失败,但第二,第三和第四遍:
//Caught type '() => dynamic' is not a subtype of type '([dynamic]) => dynamic' of 'callback'.
test('callback with optional param',() {
var thing = new Thing(() { });
thing.doCallback();
thing.doCallback('data');
});
test('callback with optional param',() {
var thing = new Thing(([_]) { });
thing.doCallback();
thing.doCallback('data');
});
test('callback with optional param',() {
var thing = new Thing();
thing.doCallback();
thing.doCallback('data');
});
test('callback with optional param',() {
var thing = new Thing(null);
thing.doCallback();
thing.doCallback('data');
});
为了跟进,我认为这种方法将把Thing的签名更改为([动态回调(),动态数据(动态值)]),以便现有的消费者仍然可以按照平时注册回调,但新消费者也可以选择进入数据通知。 – Perry 2013-04-26 17:01:35