声明式和命令式编程之间有什么区别?

问题描述

我一直在网上寻找声明式和命令式编程的定义，这将为我提供一些启发.但是，在我发现的某些资源中使用的语言令人生畏-例如在 Wikipedia .有没有人有一个真实的例子可以向我展示这个主题，也许可以带给我一些观点(也许在C#中)?

I have been searching the web looking for a definition for declarative and imperative programming that would shed some light for me. However, the language used at some of the resources that I have found is daunting - for instance at Wikipedia.Does anyone have a real-world example that they could show me that might bring some perspective to this subject (perhaps in C#)?

推荐答案

LINQ是一个很好的C#声明式与命令式编程示例.

A great C# example of declarative vs. imperative programming is LINQ.

通过命令式编程，您可以逐步告诉编译器您要发生的事情.

With imperative programming, you tell the compiler what you want to happen, step by step.

例如，让我们从这个集合开始，然后选择奇数:

For example, let's start with this collection, and choose the odd numbers:

List<int> collection = new List<int> { 1, 2, 3, 4, 5 };

使用命令式编程，我们将逐步完成并确定所需的内容:

With imperative programming, we'd step through this, and decide what we want:

List<int> results = new List<int>();
foreach(var num in collection)
{
    if (num % 2 != 0)
          results.Add(num);
}

在这里，我们是说:

1. 创建结果集合
2. 逐步浏览集合中的每个数字
3. 检查数字，如果是奇数，则将其添加到结果中

另一方面，使用声明性编程，您可以编写描述所需内容的代码，而不必描述如何获取(说明所需的结果，但不能逐步说明) :

With declarative programming, on the other hand, you write code that describes what you want, but not necessarily how to get it (declare your desired results, but not the step-by-step):

var results = collection.Where( num => num % 2 != 0);

在这里，我们说的是给我们所有奇怪的地方"，而不是逐步检查集合.请检查此项目，如果它很奇怪，请将其添加到结果集合中."

Here, we're saying "Give us everything where it's odd", not "Step through the collection. Check this item, if it's odd, add it to a result collection."

在许多情况下，代码也将是两种设计的混合体，因此它并不总是黑白的.

In many cases, code will be a mixture of both designs, too, so it's not always black-and-white.

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