Creating Indexers
The following code demonstrates how to create Indexers:
<modifier> <return type> this [argument list]
{
get
{
// your get block code
}
set
{
// your set block code
}
}
In the code above:
<modifier> can be private, public, protected or internal.
<return type> can be any valid C# types.
"this" is a special keyword in C# to indicate the object of the current class.
The formal-argument-list, that is, [argument list], specifies the parameters of the indexer.
Example Code
The code given below shows how to use Indexers:
using System;
namespace Indexer_example
{
class Program
{
class IndexerClass
{
private string[] str= new string[10];
public string this[int i]
{
get
{
return str[i];
}
set
{
str[i] = value;
}
}
}
static void Main(string[] args)
{
IndexerClass Sentence = new IndexerClass();
Sentence[0] = "Coding";
Sentence[1] = "Ninjas";
Sentence[2] = "is";
Sentence[3] = "an";
Sentence[4] = "Awesome";
Sentence[5] = "Platform";
Sentence[6] = "for";
Sentence[7] = "learning";
Sentence[8] = "and";
Sentence[9] = "coding";
for (int i = 0; i < 10; i++)
{
Console.WriteLine(Sentence[i]);
}
Console.ReadKey();
}
}
}
Overloaded Indexers
Overloaded indexers are possible. Indexers can also have multiple parameters, each of which can be of a different type. It is not required that the indexes are integers. In C#, indexes can be of any type, including strings.
Overloaded indexers are demonstrated in the following example:
using System;
namespace IndexerApplication {
class IndexedWords {
private string[] wordlist = new string[size];
static public int size = 10;
public IndexedWords() {
for (int i = 0; i < size; i++) {
wordlist[i] = "N. A.";
}
}
public string this[int index] {
get {
string tmp;
if( index >= 0 && index <= size-1 ) {
tmp = wordlist[index];
} else {
tmp = "";
}
return ( tmp );
}
set {
if( index >= 0 && index <= size-1 ) {
wordlist[index] = value;
}
}
}
public int this[string word] {
get {
int index = 0;
while(index < size) {
if (wordlist[index] == word) {
return index;
}
index++;
}
return index;
}
}
static void Main(string[] args) {
IndexedNames words = new IndexedWords();
words[0] = "Coding";
words[1] = "Ninjas";
words[2] = "is";
words[3] = "an";
words[4] = "awesome";
words[5] = "coding";
words[6] = "platform";
//using the first indexer with int parameter
for (int i = 0; i < IndexedWords.size; i++) {
Console.WriteLine(words[i]);
}
//using the second indexer with the string parameter
Console.WriteLine(words["is"]);
Console.ReadKey();
}
}
}
When the above code is compiled and run, the following is the result:
Coding
Ninjas
is
an
awesome
coding
platform
N. A.
N. A.
N. A.
2
Points to Remember
- This keyword is always used when creating indexers.
- Indexers are parameterized properties.
- Get and set accessors for the [] operator are used to implement indexers.
- Indexer does not allow ref and out parameter modifiers.
- An indexer's formal parameter list is similar to that of a method, and at least one parameter must be specified.
- Because indexer is an instance member, it cannot be static, but property can.
- On groups of elements, indexers are used.
- A property is identified by its name, whereas an indexer is identified by its signature.
- Indexes are used to access indexers, while names are used to access properties.
- The indexer can become overburdened.
Must Read IEnumerable vs IQueryable, singleton design pattern in c#
FAQs
How do get and set differ from eachother?
Get and set accessors for the [] operator are used to implement indexers. An indexer's get accessor has the same formal parameter list as the indexer itself.In addition to the value parameter, an indexer's set accessor has the same formal parameter list as the indexer. A get accessor returns a value. A set accessor assigns a value.
What does the this keyword do?
The this keyword is used to define the indexer. This keyword is not required for properties. Indexers are parameterized properties. This keyword is used to create indexers
What does the value keyword do?
The value keyword is used to define the value being assigned by the set accessor. The contextual keyword value is used in the set accessor in property and indexer declarations. It is similar to an input parameter of a method. The word value references the value that client code is attempting to assign to the property or indexer.
Is it necessary to index the indexers using integer value?
It is not necessary to index the indexers using integer values. Indexers do not have to be indexed by an integer value; how you define the specific look-up mechanism is entirely up to you.
How many formal parameters can an Indexer have?
Indexers can have more than one formal parameter. When accessing a two-dimensional array, for example, indexers can have multiple formal parameters.
Conclusion
In this article, we discussed the theoretical and practical implementation of Indexers in C#.
We hope that this blog has helped you enhance your knowledge regarding the Indexers in C# and if you would like to learn more about Methods, Type Conversions, classes and objects in C#, check out our articles on Coding Ninjas Studio. Do upvote our blog to help other ninjas grow. Happy Coding!
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