面试时问到软件开发原则，我emo了

今天去一个小公司面试，面试官是公司的软件总监，眼镜老花到看笔记本电脑困难，用win7的IE打开leetcode网页半天打不开，公司的wifi连接不上，用自己手机热点，却在笔记本电脑上找不到。还是我用自己的手机做热点，让贵公司的老古董笔记本电脑能wifi上网。然后用chrome浏览器打开了leetcode 中文网页。

Leetcode做题，毫不费劲完成了。然后面试官开始面试。第一个问题是什么是软件开发原则？我蒙圈了，说可以有各种不同的说法或解读，具体是哪个范围？他说，这个原则是统一的，是大公司google等都认可的。然后问我知不知道什么叫SRP。我都没听过。然后这个面试官不停地说这些原则多么地重要，不懂这些原则不可能团队合作，开发出高质量的大规模程序。我反问，这个有什么难度吗？我很快就可以了解。他说，这个知识点学习不难，但是真正理解，并且在项目中实施很难。然后以此为由，我作为senior programmar不胜任，面试结束。

我回家后google了software development principles，发现各种网站冒出来，五花八门的各种说法。点开了其中一个 “Foundations of Excellence: The Core Principles of Software Development”，里面提到了包括SOLID, simplicity, DRY, YAGNI: You Aren't Gonna Need It, ... 等等。其中SOLID中第一条就是SRP，single responsibility principle。我再到Youtube上搜“solid principles interview questions” ，出现的视频没有超过20多分钟的，有的只有几分钟。我点开了其中一个比较新，播放量比较高的看。SRP，简单来说，就是让你的模块和class设计功能简单化，这样的好处是比较容易维护和扩展。这其实是我以前做架构设计，开发过程中已经应用的原则，只是不知道SRR这个名字。但是现实中我看到很多代码，包括我在Apple工作期间看到的代码，明显违反了这个原则，把一大堆功能都塞到一个class里，造成可读性，可维护性很差。但是，这么多的legacy代码，而且是基础代码，也就是很多不同的应用上层代码都要调用的。除非你有充足的时间，而且有相当的容错空间，否则不可能推导重构的。另外，单一功能这种说法，本身就是一个形容词，而不是一个数量词。怎样才算单一功能，在不同的应用场景，不同人的理解，都会不一样。把class或模块的功能单一化固然可以让这个模块或class易于维护，测试和扩展。但是如果分得太细，你的程序的class和模块的数量将几何数量上升，这将导致代码的可维护性，可测试性，和可拓展性都变得非常困难。而如何找到一个平衡，本身就是要依据具体情况而定，包括任务的复杂程度，未来的路标，软件开发人员数量，水平，历史代码规模，质量，等等。
我在chatGPT上提问，

Regarding the SSR principle, though I totally agree with it, its implementation in many scenarios has no clear, rigid, and fixed lines. It depends on contexture, like requirement, and existing code base. The solution is not like solving a coding program having the unique correct answer.

得到的回答和我的观点一致：

You're absolutely correct that applying the Single Responsibility Principle (SRP), while an essential guideline for writing maintainable code, often requires context-based interpretation and doesn't have a one-size-fits-all solution. The complexity of real-world scenarios introduces nuances that make SRP less about following rigid rules and more about making thoughtful trade-offs.

Why SRP Isn't Always Clear-Cut

Context Matters:

The responsibility of a class or module often depends on:
The system's requirements.
The existing codebase's architecture.
Team conventions and project constraints.
Example: A "UserManager" class might handle authentication and profile updates in a small project. In a larger system, these might be split into separate services.

Subjectivity in Defining Responsibilities:

Responsibilities can be interpreted at different granularities.
Is "managing user data" a single responsibility or multiple ones (loading, saving, validating, etc.)?
It depends on the system's complexity and domain.

Trade-Offs with Over-Segmentation:

Overzealous adherence to SRP can lead to too many small, fragmented classes or modules, increasing complexity and reducing clarity (sometimes referred to as the "SRP trap").
Striking a balance is key: splitting responsibilities without creating unnecessary abstractions or verbosity.

Dependencies and Legacy Code:

When working with an existing codebase, introducing SRP might require significant refactoring, which may not always be feasible due to time or resource constraints.
Practical implementation often involves incremental improvements rather than a complete overhaul.

Evolving Requirements:

A responsibility that makes sense today may need to be redefined tomorrow as the system evolves. SRP requires flexibility to adapt to changes.

How to Apply SRP in Real Scenarios

Think in Terms of Change:

A good litmus test for SRP is to ask: If this class changes, why would it need to?
If a class has multiple reasons to change, it might be violating SRP.
Example: A class handling both file I/O and business logic would likely change for different reasons (e.g., a new storage format or new business rules).

Start with Clear Boundaries:

When designing new components, establish clear boundaries based on responsibilities. This is easier than retrofitting SRP into a messy, existing codebase.

Prioritize Practicality:

Don't split responsibilities for the sake of purity. Ensure that separating responsibilities adds value, such as easier testing, better readability, or more maintainability.
Example: In a small, throwaway script, strict adherence to SRP might be overkill.

Refactor Incrementally:

When working with legacy code, gradually apply SRP by:
Extracting methods or functions for secondary responsibilities.
Creating small, focused classes or modules over time.

Leverage Code Reviews and Discussions:

Use code reviews to discuss and refine the scope of responsibilities. Different perspectives can help strike the right balance.

SRP as a Guideline, Not a Rule

As you pointed out, software design doesn’t have "unique correct answers" like solving algorithmic problems. SRP is a principle to guide decision-making, not a rigid rule. The ultimate goal is to create a system that is:

Understandable: Easier for others (and your future self) to reason about.
Maintainable: Easier to update, fix, and extend.
Flexible: Adaptable to changing requirements.

By recognizing the nuances of SRP and applying it pragmatically, you can achieve these goals without being overly constrained by theoretical ideals.