# Dart Number: Double Extension

In Dart, extending the built-in `double` type directly isn't possible.

Here's why:

* **Primitive type:** `double` is a primitive type in Dart. Unlike classes, primitive types cannot be subclassed or extended.
    

Here's what you can do achieve similar functionality:

1. **Extension methods:**
    
    * While directly extending `double` isn't possible, you can achieve similar behavior using **extension methods**. Extensions allow adding methods to existing classes without modifying the original class.
        
    
    Example:
    
    Dart
    
    ```dart
    extension NumberRounding on num {
      // Rounds the number to a specified precision after the decimal point
      num toPrecision(int precision) {
        return num.parse((this).toStringAsFixed(precision));
      }
    }
    
    // Usage
    double value = 3.14159;
    double roundedValue = value.toPrecision(2); // 3.14
    ```
    
2. **Custom classes:**
    
    * If you need more complex functionality beyond simple methods, create a custom class that wraps the `double` value and provides the desired behavior.
        
    
    Example:
    
    Dart
    
    ```dart
    class MyDouble {
      final double value;
    
      MyDouble(this.value);
    
      // Add custom methods here
      double getArea() {
        // Implement area calculation based on the value
        return value * value;
      }
    }
    
    // Usage
    MyDouble areaCalculator = MyDouble(5.0);
    double area = areaCalculator.getArea(); // 25.0
    ```
    

Remember, extensions are generally preferred for adding simple methods to existing types, while custom classes are more suitable for complex functionalities.

For more information, refer to the official Dart documentation on:

* **Extension methods:** [https://dart.dev/language/extension-methods](https://dart.dev/language/extension-methods)
    
* **Numbers in Dart:** [https://dart.dev/guides/language/numbers](https://dart.dev/guides/language/numbers)