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什么是全动力闭合装置？

发布于 2024-09-09 21:01:44 字数 229 浏览 3 评论 0原文

前几天我参加了 Scala 的 Java 会议，演讲者提到了“全功能闭包”。我很难确定一个对我来说有意义的定义。我已阅读关于 closures 的维基页面，但它确实没有回答我。有人可以帮我给出一个明确的定义吗？甚至可能包括一个简单的例子。

谢谢！

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终遇你 2024-09-16 21:01:45

在计算机科学中，闭包是具有自由变量的一流函数，
被绑定在词法环境中。

除了维基百科文章中的这句话之外，您不需要更多内容。 Java 缺少的（除了丑陋的语法之外）是从闭包外部绑定自由变量的功能。一个例子：

int x = 0;
new Runnable() {
    public void run() {
        x = 1;
    }
}.run();

这里Java编译器会抱怨变量x。

同样的事情在 scala 中工作得很好，而且更简洁：

var x = 0
val fun = ()=>{x=1}
fun

In computer science, a closure is a first-class function with free variables that
are bound in the lexical environment.

You don't need more than this sentence from the wikipedia article. What Java lacks (in addition to the ugly syntax) is the feature of binding free variables from outside the closure. An example:

int x = 0;
new Runnable() {
    public void run() {
        x = 1;
    }
}.run();

Here the Java compiler will complain about the variable x.

The same thing in scala works just fine and is a lot less verbose:

var x = 0
val fun = ()=>{x=1}
fun

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梦晓ヶ微光ヅ倾城 2024-09-16 21:01:45

因为我感觉自己像个初学者（与 DPP 和 Amber 相比），所以我可能会用初学者语言向初学者解释它：

首先，匿名函数（或代码块/lambda 表达式）只是一个没有名称的函数。它可以与这样的变量绑定。

scala> val foo = (x: Int) => 2*x 
foo: (Int) => Int = <function1>

scala> val bar = foo
bar: (Int) => Int = <function1>

scala> bar(5)
res2: Int = 10

您会看到，该函数没有名称 foo，它可以从 bar 调用。

其次，闭包是一个匿名函数，它有一个未在函数内部定义的变量（变量/值必须在定义函数之前声明）。术语“全动力闭合”可能指的是这种功能。

scala> var constant = 7
constant: Int = 7

scala> val foo = (x: Int) => 2*x + constant
foo: (Int) => Int = <function1>

scala> foo(5)
res3: Int = 17

scala> constant = 6
constant: Int = 6

scala> foo(5)
res4: Int = 16

第一次看到这个，你可能想知道它有什么用处。简而言之，它有很多应用领域:-)

Since I feel like a beginner (compared to DPP and Amber) I might explain it to a beginner in a beginners language:

First, anonymous function (or code block/lambda expression) is simply a function that does not have a name. It could be tied to a variable like this.

scala> val foo = (x: Int) => 2*x 
foo: (Int) => Int = <function1>

scala> val bar = foo
bar: (Int) => Int = <function1>

scala> bar(5)
res2: Int = 10

You see, the function doesn't have the name foo, it could be called from bar instead.

Second, a closure is an anonymous function that has a variable that is not defined inside the function (the variable/value must have been declared before the function is defined). The term "full powered closure" might refer to this functionality.

scala> var constant = 7
constant: Int = 7

scala> val foo = (x: Int) => 2*x + constant
foo: (Int) => Int = <function1>

scala> foo(5)
res3: Int = 17

scala> constant = 6
constant: Int = 6

scala> foo(5)
res4: Int = 16

First time you see this, you might wonder what it is good for. In short, it has many sectors of application :-)

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