CODEWITHSUNDEEP
oopdesign-patternsobject-oriented-analysissingle-responsibility-principletell-dont-ask
Pragmatic
Pragmatic

Reputation: 3127

Single responsibility principle in API

Please have a look at following piece of code:

public interface ICultureService
{
     List<Culture> GetCultures();
     bool IsCultureSupported(Culture culture);
     Culture GetFallbackCulture();
}

We found that most of the consumers first call IsCultureSupported to validate if their culture is supported or not. And if culture is not supported, they call GetFallbackCulture():

public CallingMethod()
{
     if(!cultureManager.IsCultureSupported(currentCulture))
     {
          currentCulture=cultureManager.GetFallbackCulture();
     }
     .
     .
     .
}

As per Single Responsibility Principle (and other OOPs rules), is it ok to introduce a function (in ICultureService and its implementation) like: 

function GetFallbackCultureIfInvalid(Culture culture)
{
     if(this.IsCultureSupported(culture)
     {
          return this.FallbackCulture();
     }
}

Upvotes: 0

Views: 1039

Answers (1)

Chetan Kinger
Chetan Kinger

Reputation: 15212

As per Single Responsibility Principle (and other OOPs rules), is it ok to introduce a function (in CultureManager) like:

What you are referring to is called the Tell-Don't-Ask principle rather than the Single Responsibility Principle. Adding the GetFallbackCultureIfInvalid function actually makes the client code more readable. You should also reduce the visibility of the IsCultureSupported so that this method is no longer visible to the client code.

That said, it looks like CultureManager is an implementation of CultureService so it doesn't make sense to add a new method named GetFallbackCultureIfInvalid in CultureManager which is not a part of CultureService interface. What you should do is stick to a single method called GetFallbackCulture in CultureManager and let it return a fall back culture if the required condition is met :

Culture GetFallbackCulture(Culture culture) {
    Culture fallBackCulture = culture;
    if(!this.IsCultureSupported(culture) {
      fallBackCulture = this.FallbackCulture();
    } 

    return fallBackCulture;
}

Upvotes: 0

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