# 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](https://maximilianocontieri.com/the-one-and-only-software-design-principle)

- Validated strings are a subset of all possible strings.

- [Fail Fast](https://maximilianocontieri.com/fail-fast) principle violation.

- Single Responsibility Principle violation.

- DRY Principle Violation.

# Solutions

1. Create a first-class object representing the concept under the [MAPPER](https://maximilianocontieri.com/what-is-wrong-with-software)

# 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

[Gist Url]: # (https://gist.github.com/mcsee/1b6799dac071ce8bd2a1082dfdbd668d)
```php
<?

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

[Gist Url]: # (https://gist.github.com/mcsee/d2eace32ecb9f7564ebeaf8136118f53)
```php
<?

//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);
    }   
    $this->address = $emailAddress;
  }
}

//Second Example: Wordle

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

class WordleWord { 
  function __construct(string $emailAddress)
    //Avoid building invalid world words
    //For example length != 5
  }
 }
```

# Detection

[X] Semi-Automatic 

We can check all constructors validating strings and [reify](https://en.wikipedia.org/wiki/Reification_%28computer_science%29) the missing concepts.

# Tags

- Primitive Obsession

# Conclusion

Small objects are hard to find.

Primitive obsessors [always complain](https://maximilianocontieri.com/i-wrote-more-than-90-articles-on-2021-here-is-what-i-learned) about this kind of indirections.

Creating these new small concepts keeps our model loyal to the bijection and ensures our models are always healthy.

# Relations

%[https://maximilianocontieri.com/code-smell-41-regular-expression-abusers]

%[https://maximilianocontieri.com/code-smell-04-string-abusers]

# More Info

- [The One and Only Software Design Principle](https://maximilianocontieri.com/the-one-and-only-software-design-principle)

- [How to Develop a Wordle Game](https://maximilianocontieri.com/how-to-develop-a-wordle-game-using-tdd-in-25-minutes)

- [Object Reification](https://en.wikipedia.org/wiki/Reification_%28computer_science%29)

# Credits

Photo by [Brett Jordan](https://unsplash.com/@brett_jordan) on [Unsplash](https://unsplash.com/s/photos/letters)
  
* * *

> Less than 10% of the code has to do with the ostensible purpose of the system; the rest deals with input-output, data validation, data structure maintenance, and other housekeeping.

_Mary Shaw_
 
%[https://maximilianocontieri.com/software-engineering-great-quotes]

* * *

This article is part of the CodeSmell Series.

%[https://maximilianocontieri.com/how-to-find-the-stinky-parts-of-your-code]