The S of SOLID in my view.

Witerlland Silva — Wed, 07 Feb 2024 17:26:03 +0000

Hi, This is my first article on this site. This is my first article at all. So, in this series of articles, I want to review SOLID with Typescript. To start this series, of course, I want to talk about the S of SOLID (Single responsible principle). Uncle Bob says in the book Clean Architecture, 2019: "A module should be responsible to one, and only one, actor." This is because the name of the principle causes a lot of mistakes for programmers; they think something like that: "A class should do one thing."

But I think in this case, the correct answer is something like that: A class should only do one thing related to the actor or change only when this actor requests a change. The actor is related to users or stakeholders, and that's the point: a software or class only needs to change when these actors request a change.

So, here we can see several problems that we can solve by using that principle, like:

Lack of cohesion.
High coupling.
Testing is hard.
Reusing of code is too hard.

Let's go to examples.

Imagine a class that emits reports.

class ReportService { 
  constructor(private apiEndpoint: string) {}
  public getReport(): any { 
    const salesReport = this.apiRequest('/sales'); 
    const sellersReport = this.apiRequest('/sellers'); 
    const billingsReport = this.apiRequest('/billings'); 
    return {
      salesReport, 
      sellersReport, 
      billingsReport,
    };
  }
  private apiRequest(endpoint: string): any {
    // Request 
  }
}

In this case, the class emits three reports: Sales, Sellers and billings. In this class, we have a method to request a report from the API and one method to export the report requested.Take a look; we have three actors here: The financial sector, the people sector, and a sector of sales. Imagine if one of these actors requests a change; all the classes need to change at the same time. And this causes a lot of work.

Take note: To solve this problem, we need to split responsibility. Making three classes, one for each actor.

Examples:

class salesReportService{ 
  constructor(private apiEndpoint: string) {}
  public getReport(): any { 
    return this.apiRequest('/sales'); 
  }
  private apiRequest(endpoint: string): any {
    // Request 
  }

}

class sellersReportService{ 
  constructor(private apiEndpoint: string) {}
  public getReport(): any {
    return this.apiRequest('/sellers'); 
  }
  private apiRequest(endpoint: string): any {
    // Request 
  }

}

class billingsReportService{ 
  constructor(private apiEndpoint: string) {}
  public getReport(): any {
    return this.apiRequest('/billings'); 
  }
  private apiRequest(endpoint: string): any {
    // Request 
  }

}

Well. I think that's it. Sorry for any error, and feel free to correct me any time.

Forem: Witerlland Silva

The S of SOLID in my view.