Code Smell 121 - String Validations

You need to validate strings. So you don't need strings at all

TL;DR: Search for missing domain objects when validating strings.

Problems

Primitive obsession.
Bijection Fault
Validated strings are a subset of all possible strings.
Fail Fast principle violation.
Single Responsibility Principle violation.
DRY Principle Violation.

Solutions

Create a first-class object representing the concept under the MAPPER

Context

Serious software has lots of string validations.

Often, They are not in the correct places.

This leads to non-robust and corrupt software.

The simple solution is to build only real-world and valid abstractions.

Sample Code

Wrong

<?

//First Example: Address Validation
class Address { 
  function __construct(string $emailAddress) {
     //String validation on Address class violates SRP
     $this->validateEmail($emailAdress);
     //...
   }

  private function validateEmail(string $emailAddress) {
    $regex = "/[a-zA-Z0-9_-.+]+@[a-zA-Z0-9-]+.[a-zA-Z]+/";
    //Regex is a sample / It might be wrong
    //Emails and Urls should be first class objects

    if (!preg_match($regex, $emailAddress))
    {
      throw new Exception('Invalid email address ' . emailAddress);
    }    
  }
}

//Second Example: Wordle

class Wordle { 
  function validateWord(string $wordleword){
    //Wordle word should be a real world entity. Not a subset of strings
  }
 }

Right

<?

//First Example: Address Validation
class Address { 
  function __construct(EmailAddress $emailAddress) {
     //Email is always valid / Code is cleaner     
     //...
   }
}

class EmailAddress { 
  //We can reuse this object many times avoiding copypasting
  string $address; 
  private function __construct(string $emailAddress) {
    $regex = "/[a-zA-Z0-9_-.+]+@[a-zA-Z0-9-]+.[a-zA-Z]+/";
    //Regex is a sample / It might be wrong
    //Emails and Urls are first class objects

    if (!preg_match($regex, $emailAddress))
    {
      throw new Exception('Invalid email address ' . emailAddress);
    }