避免在工厂类中使用多个if-else语句[与语言无关] [英] Avoid multiple if-else statements in a factory class [language agnostic]

问题描述

我有一些要筛选的数据，我想不出一个聪明的方法。假设我有3种类型：

I have some data that I'm trying to sift through and I can't figure out a smart way of doing this. Let's say I have 3 types:

A，B，C，它们都扩展了类S。

A, B, C and they all extend a class S.

如果我创建一个仅创建并返回类型为S的对象的工厂，那么这看起来将是非常程序化的。工厂在伪代码中的实现如下所示：

If I create a factory that just creates and returns and object of type S, it seems like it would be very procedural. The factory's implementation in pseudo-code would be something like this:

class Factory {
    func create_obj(input_data) -> S {
        if type(input_data) is A {
            return A()
        }
        else if type(input_data) is B {
            return B()
        }
        else {
            return C()
        }
    }
}

现在，我可能有很多不同的数据类型。这意味着该算法在最坏的情况下处于二次时间。有没有更好的解决方案，设计模式或我可以查看的任何优化？更具体地说，我正在创建某些数据类型的实例，并且输入为文本行。

Now, I have a lot of different data types that it could possibly be. That means this algorithm in the worst case is in quadratic time. Is there a better solution, design pattern, or any optimizations I can look at? To be more specific, I'm creating instances of certain data types and the input is lines of text.

推荐答案

解决该问题的一种方法是使用预先填充的关联数组，其中键是字符串表示文件中的行/值，该值是应为该行返回的对象。

One way to approach the problem would be to use a pre-populated associative array where the key is a string representing a line/value in the file and the value is the object that should be returned for that line.

示例实现：

让文件是一个关联数组。在启动时，工厂应使用 string 将该对象预填充到对象映射：

Let file be an asscociateive array. On startup, the factory should pre-populate this array with string to object mappings :

files["A"] = new A();
files["B"] = new B();
files["C"] = new C();

然后可以给工厂传递一个 string ，它将在关联数组以获取相应的预填充对象：

The factory can then be passed a string which it will lookup in the associative array to fetch the corresponding pre-populated object :

func create_obj(input_data) -> S {
   return files[input_data];
}

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