Question

How can I override operators to be used on builtin types like String, arrays etc? For example: I wish to override the meaining of the + operator for arrays.

Answer 1

You can’t overload operators for existing types, as that could potentially break any other code that uses the types.

You can make your own class that encapsulates an array, expose the methods and properties that you need from the array, and overload any operators that makes sense.

Example:

public class AddableArray<T> : IEnumerable<T> {      private T[] _array;      public AddableArray(int len) {         _array = new T[len];     }      public AddableArray(params T[] values) : this((IEnumerable<T>)values) {}      public AddableArray(IEnumerable<T> values) {         int len;         if (values is ICollection<T>) {             len = ((ICollection<T>)values).Count;         } else {             len = values.Count();         }         _array = new T[len];         int pos = 0;         foreach (T value in values) {             _array[pos] = value;             pos++;         }     }      public int Length { get { return _array.Length; } }      public T this[int index] {         get { return _array[index]; }         set { _array[index] = value; }     }      public static AddableArray<T> operator +(AddableArray<T> a1, AddableArray<T> a2) {         int len1 = a1.Length;         int len2 = a2.Length;         AddableArray<T> result = new AddableArray<T>(len1 + len2);         for (int i = 0; i < len1; i++) {             result[i] = a1[i];         }         for (int i = 0; i < len2; i++) {             result[len1 + i] = a2[i];         }         return result;     }      public IEnumerator<T> GetEnumerator() {         foreach (T value in _array) {             yield return value;         }     }      IEnumerator System.Collections.IEnumerable.GetEnumerator() {         return _array.GetEnumerator();     }  } 

Usage:

// create two arrays AddableArray<int> a1 = new AddableArray<int>(1, 2, 3); AddableArray<int> a2 = new AddableArray<int>(4, 5, 6);  // add them AddableArray<int> result = a1 + a2;  // display the result Console.WriteLine(string.Join(', ', result.Select(n=>n.ToString()).ToArray())); 

(Note that as the class implements IEnumerable<T>, you can use extension methods like Select on it.)