Chapter 10 - Indexers

Indexers 1C# 30

C# 3.0C# 3.0

Chapter 10 Indexers

Copyright SELA Software & Education Labs Ltd. 14-18 Baruch Hirsch St. Bnei Brak 51202 Israel

Indexers MotivationIndexers 2C# 30

Indexers MotivationTo enable a container class to pro ide To enable a container class to provide intuitive access to its elements, C# offers an indexer

Indexers allow you to index a class or a struct Indexers allow you to index a class or a structinstance in the same way as an arrayF l k i b l i f ti i t For example: keeping boolean information in compact bit storage, while exposing it, through an indexer, as an array of bool elementsan array of bool elements

The C++ equivalent is the [] operatorq [] p


An Indexer ExampleIndexers 3C# 30

An Indexer Example Assume the following EmployeeManager Assume the following EmployeeManager

class that stores employeesp yclassEmployeeManager{{

privateint _numEmployees =0;privateEmployee[]_employees;

publicint NumEmployeespublicEmployeeManager(int maxEmployees)publicEmployeeManager(int maxEmployees)publicbool Add(Employeee)publicvoidSortByName()publicvoidSortBySalary()publicvoidPrint()

}


}

An Indexer ExampleIndexers 4C# 30

An Indexer Example

publicEmployeethis[int index]{

getget{if(index=_numEmployees)

returnnull;returnnull;else

return_employees[index];}set{{if(!(index=_numEmployees))

_employees[index]=value;}}

}


An Indexer Example UsageIndexers 5C# 30

An Indexer Example UsageEmployeee1=newEmployee("Jack");Employeee1 newEmployee( Jack );Employeee3=newEmployee("Dave");EmployeesManager employees=newEmployeesManager(10);Employees.Add(e1);employees.Add(e2);

()employees.SortByName();employees.Print();//Herecomestheinterestingpart://Herecomestheinterestingpart:for(int i =0;i

Indexer Declaration RulesIndexers 7C# 30

Indexer Declaration RulesThe inde er bod sho ld be comprised of The indexer body should be comprised of get and set assessorsg Providing only a get or a set assessors will result in

a read-only or a write-only indexera read only or a write only indexerThe System.String class indexer, for example, is read-only, as strings are immutabley, g

Indexers can be overloaded: You can define more than one indexer for a class, as

long as they differ in their parameter lists


Indexers Under the HoodIndexers 8C# 30

Indexers Under the Hood Indexers are special case of properties Indexers are special case of properties.propertyinstanceclassEmployeeItem(int32)

Lets look at their metadata definition:p p y p y ( )

{.getinstanceclassEmployeeEmployeesManager::get_Item(int32).setinstancevoidEmployeesManager::set Item(int32,classEmployee).setinstancevoidEmployeesManager::set_Item(int32,classEmployee)

}//endofpropertyEmployeesManager::Item

In C#, the name of the property is Item The getter name is get Itemg g _

It receives one input parameter: the index The setter name is set_Item_

It receives two input parameters: the index & the value


Indexers 9C# 30

Chapter 10 Exercise 1

THE WEEKLY SCHEDULE EXERCISEEXERCISE


SummaryIndexers 10C# 30

Summary Following are some of the indexers special Following are some of the indexers special

characteristics: They have (in C#) an hard coded name: Item They have an optional (greater than zero) number of

parameters They are accessed through the array element access[] t[]syntax

They are identified by their signature Properties are defined by their name

Indexers must be instance membersP ti b ith i t t ti b Properties can be either instance or static members


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Chapter 10 - Indexers