scala.util.Failure 声明如下:
final case class Failure[+T](exception: Throwable) extends Try[T]`
它需要一个T看起来完全不必要的类型参数,给出如何Failure轻松地声明为子类型Try[Nothing]:
final case class Failure(exception: Throwable) extends Try[Nothing]`
以与None声明相同的方式:
object None extends Option[Nothing]
实际上,额外的类型参数在其他地方成为痛点.这是Future.zip:
def zip[U](that: Future[U]): Future[(T, U)] = {
implicit val ec = internalExecutor
val p = Promise[(T, U)]()
onComplete {
case f: Failure[_] => p complete f.asInstanceOf[Failure[(T, U)]]
case Success(s) => that onComplete { c => p.complete(c map { s2 => (s, s2) }) }
}
p.future
} …这两个表达式应该是一样的:
Stream.from(1).filter(_ < 0).head
Stream.from(1).find(_ < 0)
应该循环直到它们返回Int.MinValue.这正是版本所具有的filter功能,但是产生了find一个版本OutOfMemoryError.看看他们的实现,我无法弄清楚这两个版本都没有产生OutOfMemoryError.
这是执行Stream.filter:
override def filter(p: A => Boolean): Stream[A] = {
// optimization: drop leading prefix of elems for which f returns false
// var rest = this dropWhile (!p(_)) - forget DRY principle - GC can't collect otherwise
var rest = this
while (!rest.isEmpty && !p(rest.head)) rest = rest.tail
// private utility func to avoid `this` on stack (would be …我正在使用泰坦尼克号数据集，并尝试针对分类变量生成一对数值变量图。我可以使用 Seaborn'scatplot绘制一个数字变量与一个分类变量的图：
import seaborn as sns
sns.catplot(data=train, x='Fare', y='Sex')
但是，如果我尝试使用 PairGrid 根据分类变量绘制数字变量：
x_vars = ['Fare']
y_vars = ['Sex']
g = sns.PairGrid(train, x_vars=x_vars, y_vars=y_vars)
g.map(sns.catplot)
它失败并出现错误：
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-75-c284a7cfd727> in <module>
9 #g.map_diag(lambda x, **kwargs: sns.catplot(x, x, **kwargs), jitter=True, kind="bar")
10 #g.map(sns.scatterplot, y_jitter=1)#, hue=train["Survived"])
---> 11 g.map(sns.catplot)#, hue=train["Survived"])
~/MLProject/book1/lib/python3.8/site-packages/seaborn/axisgrid.py in map(self, func, **kwargs)
1363 row_indices, col_indices = np.indices(self.axes.shape)
1364 indices = zip(row_indices.flat, col_indices.flat)
-> 1365 self._map_bivariate(func, indices, **kwargs)
1366 return self
1367
~/MLProject/book1/lib/python3.8/site-packages/seaborn/axisgrid.py in …我正在尝试使用Fuse迭代器适配器并获得意外结果(Playground链接):
fn main() {
let mut i1 = (1..3).scan(1, |_, x| {
if x < 2 { None } else { Some(x) }
});
println!("{:?}", i1.next());
println!("{:?}", i1.next());
println!("{:?}", i1.next());
println!("");
let mut i2 = (1..3).scan(1, |_, x| {
if x < 2 { None } else { Some(x) }
}).fuse();
println!("{:?}", i2.next());
println!("{:?}", i2.next()); // This should print None
println!("{:?}", i2.next());
println!("");
}
哪个印刷品:
None
Some(2)
None
None
Some(2)
None
迭代器i1正在回归我的期望.它返回None,然后 …
我做了一个非常基本的喷雾测试,使用:
这是我的代码:
val myListener: ActorRef = system.actorOf(Props[TestHttpListener], "httpListener")
IO(Http) ! Http.Bind(myListener, interface = "localhost", port = 8080)
该httpListener起反应对Http.Connected用Http.Register(self).
我使用sbt来运行我的代码.它失败了AbstractMethodError:
[ERROR] [07/12/2014 18:46:48.364] [default-akka.actor.default-dispatcher-5] [ActorSystem(default)] Uncaught error from thread [default-akka.actor.default-dispatcher-5] shutting down JVM since 'akka.jvm-exit-on-fatal-error' is enabled
java.lang.AbstractMethodError: spray.can.HttpManager.akka$actor$ActorLogging$_setter_$log_$eq(Lakka/event/LoggingAdapter;)V
at akka.actor.ActorLogging$class.$init$(Actor.scala:335)
at spray.can.HttpManager.<init>(HttpManager.scala:29)
at spray.can.HttpExt$$anonfun$1.apply(Http.scala:153)
at spray.can.HttpExt$$anonfun$1.apply(Http.scala:153)
at akka.actor.TypedCreatorFunctionConsumer.produce(Props.scala:422)
at akka.actor.Props.newActor(Props.scala:331)
at akka.actor.ActorCell.newActor(ActorCell.scala:534)
at akka.actor.ActorCell.create(ActorCell.scala:560)
at akka.actor.dungeon.FaultHandling$class.finishCreate(FaultHandling.scala:135)
at akka.actor.dungeon.FaultHandling$class.faultCreate(FaultHandling.scala:129)
at akka.actor.ActorCell.faultCreate(ActorCell.scala:338)
at akka.actor.dungeon.FaultHandling$class.faultRecreate(FaultHandling.scala:58)
at …考虑这个代码：
struct WithLifetime<'a> {
s: &'a str
}
impl WithLifetime<'_> {
fn in_impl(&self) -> bool {
self.s == "a"
}
}
fn out_of_impl(wl: &WithLifetime<'_>) -> bool {
wl.s == "a"
}
fn higher_order(f: fn(&WithLifetime<'_>) -> bool) -> bool {
let s = "a";
let wl = WithLifetime { s };
f(&wl)
}
fn main() {
higher_order(out_of_impl); // This line compiles
higher_order(WithLifetime::in_impl); // This line does not
}
最后一行main由于此错误而无法编译：
error[E0308]: mismatched types
--> src/main.rs:23:18
|
23 | higher_order(WithLifetime::in_impl); // …我想要一个仅在选中一组复选框中的一个时才启用的按钮,类似于http://jsfiddle.net/chriscoyier/BPhZe/76中的小提琴:
var checkboxes = $("input[type='checkbox']"),
submitButt = $("input[type='submit']");
checkboxes.click(function() {
submitButt.attr("disabled", !checkboxes.is(":checked"));
});
我想用AngularJs来实现它.
由于某种原因,以下代码无法访问.我无法理解为什么我的代码永远不会到达,因为这是一个简单的模式匹配.这里是:
type Occurrences = List[(Char, Int)]
def combinations(occurrences: Occurrences): List[Occurrences] = occurrences match{
case Nil => Nil
case List() => List()
case x => List(x)
case x::xs => combinations(List((x._1,x._2 - 1))) ::: combinations(xs)
}
该算法旨在提取给定列表的所有子列表.
下面的代码：
trait t1 {
def printt1 = println("In t1")
}
trait t2 {
def printt1 = println("In t2")
}
class cclass extends t1 with t2
导致此编译时错误：
class cclass inherits conflicting members: method printt1 in trait t1 of type => Unit and method printt1 in trait t2
of type => Unit (Note: this can be resolved by declaring an override in class cclass.)
因此，这提供了编译时检查，该检查不允许多重继承，但允许混合，同时还可以防止Diamond问题：“多年来，多重继承一直是一个棘手的问题[需要引用]，反对者指出它的复杂性和歧义性越来越高。 “钻石问题”之类的情况，如果一个以上的父类实现了某个特定功能，则该特定功能是从哪个父类继承的就可能是模棱两可的。” 来源：http : //en.wikipedia.org/wiki/Multiple_inheritance
为了解决上面的编译时错误，我只是重写t1：
class cclass extends t1 with t2 {
override def printt1 = …