Difference between Single Responsibility Principle and Separation of Concerns

Question

What is the difference between Single Responsibility Principle and Separation of Concerns?

Answer 1

Answer:

Separation of Concerns (SoC) is a more versatile term - it can be applied at the system level or at lower levels such as classes (or even the methods within a class)

Single Responsibility Principle (SRP) is used to discuss SoC at the lower levels e.g. in a class

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Ways to think about it:

1. At the low level, SoC and SRP are synonymous. So you could say SRP is a redundant term - or that SoC should only be used to discuss the system level

2. Given (1), the term SoC is somewhat ambiguous. You need context to know whether the discussion is about high level SoC or lower level SoC

3. To remember that SRP is the term for only lower levels, think of this: in everyday language, a "responsibility" is usually a well-defined thing that can be tied to specific code, whereas "concerns" are usually kind of vague and may encompass a bunch of related things, which is perhaps why SoC is a more natural fit for discussing the system level than is SRP

4. SoC is in some sense a stronger requirement/principle than SRP because it applies at the system level, and to be truly achieved at the system level must also be used in the development of the system components. That is, a high level of SoC implies decent SoC/SRP at the lower levels - but the reverse is not true, that is, lower level SoC/SRP does not imply SoC or anything at all for the next higher level, never mind the encompassing system. For an example of SoC/SRP that is achieved at the method level, but then violated at the class level, check out this Artur Trosin's blog post.