How do I overload the square-bracket operator in C#?

Coderer_26286 0
Viewed 141868

DataGridView, for example, lets you do this:

DataGridView dgv = ...;
DataGridViewCell cell = dgv[1,5];

but for the life of me I can't find the documentation on the index/square-bracket operator. What do they call it? Where is it implemented? Can it throw? How can I do the same thing in my own classes?

ETA: Thanks for all the quick answers. Briefly: the relevant documentation is under the "Item" property; the way to overload is by declaring a property like public object this[int x, int y]{ get{...}; set{...} }; the indexer for DataGridView does not throw, at least according to the documentation. It doesn't mention what happens if you supply invalid coordinates.

ETA Again: OK, even though the documentation makes no mention of it (naughty Microsoft!), it turns out that the indexer for DataGridView will in fact throw an ArgumentOutOfRangeException if you supply it with invalid coordinates. Fair warning.

collections operator-overloading operators c#
8 Answers

you can find how to do it here. In short it is:

public object this[int i]
{
    get { return InnerList[i]; }
    set { InnerList[i] = value; }
}

If you only need a getter the syntax in answer below can be used as well (starting from C# 6).

Ruben_217330
Ricardo_Villamil_193140 
Operators                           Overloadability

+, -, *, /, %, &, |, <<, >>         All C# binary operators can be overloaded.

+, -, !,  ~, ++, --, true, false    All C# unary operators can be overloaded.

==, !=, <, >, <= , >=               All relational operators can be overloaded, 
                                    but only as pairs.

&&, ||                              They can't be overloaded

() (Conversion operator)            They can't be overloaded

+=, -=, *=, /=, %=                  These compound assignment operators can be 
                                    overloaded. But in C#, these operators are
                                    automatically overloaded when the respective
                                    binary operator is overloaded.

=, . , ?:, ->, new, is, as, sizeof  These operators can't be overloaded

    [ ]                             Can be overloaded but not always!

Source of the information

For bracket:

public Object this[int index]
{
    
}

##BUT

The array indexing operator cannot be overloaded; however, types can define indexers, properties that take one or more parameters. Indexer parameters are enclosed in square brackets, just like array indices, but indexer parameters can be declared to be of any type (unlike array indices, which must be integral).

From MSDN

Daok_139130 
public class CustomCollection : List<Object>
{
    public Object this[int index]
    {
        // ...
    }
}
user_188110

Here is an example returning a value from an internal List object. Should give you the idea.

  public object this[int index]
  {
     get { return ( List[index] ); }
     set { List[index] = value; }
  }
user_308270

For CLI C++ (compiled with /clr) see this MSDN link.

In short, a property can be given the name "default":

ref class Class
{
 public:
  property System::String^ default[int i]
  {
    System::String^ get(int i) { return "hello world"; }
  }
};
Admin1

If you mean the array indexer,, You overload that just by writing an indexer property.. And you can overload, (write as many as you want) indexer properties as long as each one has a different parameter signature

public class EmployeeCollection: List<Employee>
{
    public Employee this[int employeeId]
    {   
        get 
        { 
            foreach(var emp in this)
            {
                if (emp.EmployeeId == employeeId)
                    return emp;
            }

            return null;
        }
    }

    public Employee this[string employeeName]
    {   
        get 
        { 
            foreach(var emp in this)
            {
                if (emp.Name == employeeName)
                    return emp;
            }

            return null;
        }
    }
}
user_326320
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