Scala 中的应用和 lambdas [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 !

我想实际上就像

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

发生了.谁能向我解释为什么会发生这种情况，或者如果我错了，究竟会发生什么?

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

推荐答案

为了了解发生了什么，我使用了我的小工具 scala-to-java.

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

您转换为 Java 的代码如下所示:

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，也就是 StringBuilder 被简单地转换为 Function1并用作 foreach 中的函数参数.

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)
• 序列(scala.collection)
• 偏函数(scala)
• 函数 1 (scala)

总结:

• 您可以使用任何 StringBuilder 作为函数或部分函数，​​从 Int 到 Char
• 在您的情况下，append 只计算一次，其结果 (StringBuilder) 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.

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