在Scala中套用和Lambda [英] Apply and lambdas in Scala

问题描述

我有以下一段代码

scala> val builder = new StringBuilder("foo bar baz ")
builder: StringBuilder = foo bar baz

scala> (0 until 5) foreach { builder.append("!") }

scala> builder.toString
res15: String = foo bar baz !

我想实际上是这样的

(0 until 5) foreach builder.append("!").apply

发生.谁能向我解释为什么会发生这种情况，或者如果我错了，真正发生的事情是什么?

happens. Can anyone explain to me why that happens or if I'm wrong what really happens?

推荐答案

要了解正在发生的事情，我使用了我的小型工具 scala-到Java .

To understand what's happening I used my small tool scala-to-java.

您转译为Java的代码如下:

Your code transpiled to Java looks like this:

public final class _$$anon$1 {
  private final StringBuilder builder = new StringBuilder("foo bar baz ");

  private StringBuilder builder() {
    return this.builder;
  }

  {
    RichInt$.MODULE$.until$extension0(Predef$.MODULE$.intWrapper(0), 5).foreach((Function1<Object, Object>)this.builder().append("!"));
    this.builder().toString();
  }
}

如您所见，

builder.append("!")的结果(也为StringBuilder)被简单地转换为Function1并在foreach中用作函数参数.

As you can see, result of the builder.append("!"), which is also StringBuilder is simply cast to Function1 and used as a function argument in foreach.

显然，StringBuilder确实是一个函数，如果您检查它的类型层次结构:

Apparently, StringBuilder is indeed a function, if you check it's type hierarchy:

• StringBuilder(scala.collection.mutable)
• AbstractSeq(scala.collection.mutable)
• AbstractSeq(scala.collection)
• Seq(scala.collection)
• PartialFunction(标量)
• Function1(标量)

结论:

• 您可以使用任何StringBuilder作为从Int到Char
的函数或部分函数
• 在您的情况下，append仅被评估一次，其结果(StringBuilder)被用作函数.

• You can use any StringBuilder as an function or partial function from Int to Char
• In your case, append is evaluated only once and it's result (StringBuilder) is used as a function.

这篇关于在Scala中套用和Lambda的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！