string.IsNullOrEmpty（myString）或string.IsNullOrWhiteSpace（myString）是否违反了SRP规则？

Question

As the question shows,

As we are using string functions like IsNullOrEmpty or IsNullOrWhiteSpace as the name of functions shows , these are doing more than one job , is it not a violation of SRP ?

rather should it not be string.isValid(Enum typeofValidation) than using strategey pattern to choose the correct strategey to validate.

or is it perfectly OK to violate SRP in utilities class or static classes.

Answer 1

The SRP says that a function or class should have only one reason to change. What is a reason to change? A reason to change is a user who requests changes. So a class or function should have only one user who requests changes.

Now a function that does some calculations and then some formatting, has two different users that could request a change. One would request changes to the calculations and the other would request changes to the formatting. Since these users have different needs and will make their requests and different times, we'd like them to be served by different functions.

IsNullOrEmpty(String) is not likely to be serving two different users. The user who cares about null is likely the same user who cares about empty, so isNullOrEmpty does not violate the SRP.

Answer 2

In object-oriented programming, the single responsibility principle states that every object should have a single responsibility

You're describing methods: IsNullOrEmpty or IsNullOrWhiteSpace, which are also self-describing in what they do, they're not objects. string has a single responsibility - to be responsible for text strings!

Static helpers can perform many tasks if you choose: the whole point of the Single Responsibility principle is to ultimately make your code more maintainable and readable for future teams and yourself. As a comment says, don't overthink it. You're not designing the framework here but just consuming some parts of it that will clean your strings for you, and validate incoming data.

Answer 3

The SRP applies to classes, not methods. Still, it's a good idea to have methods that do one thing only. But you can't take that to extremes. For example, a console application would be fairly useless if its Main method could contain only one statement (and, if the statement is a method call, that method could also contain only one statement, etc., recursively).

Think about the implementation of IsNullOrEmpty:

static bool IsNullOrEmpty(string s)
{
    return ReferenceEquals(s, null) || Equals(s, string.Empty);
}

So, yes, it's doing two things, but they're done in a single expression. If you go to the level of expressions, any boolean expression involving binary boolean operators could be said to be "doing more than one thing" because it is evaluating the truth of more than one condition.

If the names of the methods bother you because they imply too much activity for a single method, wrap them in your own methods with names that imply the evaluation of a single condition. For example:

static bool HasNoVisibleCharacters(string s) { return string.IsNullOrWhitespace(s); }
static bool HasNoCharacters(string s) { return string.IsNullOrEmpty(s); }

In response to your comment:

say I wrote the function like SerilizeAndValidate(ObjectToSerilizeAndValidate) , clearly this method / class , is doing 2 things , Serialize and Validation, clearly a violation , some time methods in a class leads to maintenance nightmare like above example of serialize and validation

Yes, you are right to be concerned about this, but again, you cannot literally have methods that do one thing only. Remember that different methods will deal with different levels of abstraction. You might have a very high-level method that calls SerializeAndValidate as part of a long sequence of actions. At that level of abstraction, it might be very reasonable to think of SerializeAndValidate as a single action.

Imagine writing a set of step-by-step instructions for an experienced user to open a file's "properties" dialogue:

• Right-click the file
• Choose "Properties"

Now imagine writing the same instructions for someone who's never used a mouse before:

• Position the mouse pointer over the file's icon
• Press and release the right mouse button
• A menu appears. Position the mouse pointer over the word "Properties"
• Press and release the left mouse button

When we write computer programs, we need to operate at both levels of abstraction. Or, rather, at any given time, we're operating at one level of abstraction or another, so as not to confuse ourselves. Furthermore, we rely on library code that operates at lower levels of abstraction still.

Methods also allow you to comply with the "do not repeat yourself" principle (often known as "DRY"). If you need to both serialize and validate objects in many parts of your application, you'd want to have a SerializeAndValidate method to reduce duplicative code. You'd be very well advised to implement the method as a simple convenience method:

void SerializeAndValidate(SomeClass obj)
{
    Serialize(obj);
    Validate(obj);
}

This allows you the convenience of calling one method, while preserving the separation of serialization logic from validation logic, which should make the program easier to maintain.

Answer 4

I don't see this as doing more than one thing. It is just making sure your string passes a required condition.