Dart Programming - Generics | Adglob Infosystem Pvt Ltd

In this guide, we will discuss Generics in Dart Programming Language. Dart is an optionally typed language. Collections in Dart are heterogeneous by default. In other words, a single Dart collection can host values of various types. However, a Dart collection can be made to hold homogenous values. The concept of Generics can be used to achieve the same.

The use of Generics enforces a restriction on the data type of the values that can be contained by the collection. Such collections are termed as type-safe collections. Type safety is a programming feature which ensures that a memory block can only contain data of a specific data type.

All Dart collections support type-safety implementation via generics. A pair of angular brackets containing the data type is used to declare a type-safe collection. The syntax for declaring a type-safe collection is as given below.

Syntax

Collection_name <data_type> identifier= new Collection_name<data_type>

The type-safe implementations of List, Map, Set and Queue is given below. This feature is also supported by all implementations of the above-mentioned collection types.

Example: Generic List

void main() { 
   List <String> logTypes = new List <String>(); 
   logTypes.add("WARNING"); 
   logTypes.add("ERROR"); 
   logTypes.add("INFO");  
   
   // iterating across list 
   for (String type in logTypes) { 
      print(type); 
   } 
}

It should produce the following output −

WARNING 
ERROR 
INFO

An attempt to insert a value other than the specified type will result in a compilation error. The following example illustrates this.

Example

void main() { 
   List <String> logTypes = new List <String>(); 
   logTypes.add(1); 
   logTypes.add("ERROR"); 
   logTypes.add("INFO"); 
  
   //iterating across list 
   for (String type in logTypes) { 
      print(type); 
   } 
}

It should produce the following output −

1                                                                                     
ERROR                                                                             
INFO

Example: Generic Set

void main() { 
   Set <int>numberSet = new  Set<int>(); 
   numberSet.add(100); 
   numberSet.add(20); 
   numberSet.add(5); 
   numberSet.add(60);
   numberSet.add(70); 
   
   // numberSet.add("Tom"); 
   compilation error; 
   print("Default implementation  :${numberSet.runtimeType}");  
   
   for(var no in numberSet) { 
      print(no); 
   } 
}

It should produce the following output −

Default implementation :_CompactLinkedHashSet<int> 
100 
20 
5 
60 
70

Example: Generic Queue

import 'dart:collection'; 
void main() { 
   Queue<int> queue = new Queue<int>(); 
   print("Default implementation ${queue.runtimeType}");  
   queue.addLast(10); 
   queue.addLast(20); 
   queue.addLast(30); 
   queue.addLast(40); 
   queue.removeFirst();  
   
   for(int no in queue){ 
      print(no); 
   } 
}

It should produce the following output −

Default implementation ListQueue<int> 
20 
30 
40

Generic Map

A type-safe map declaration specifies the data types of −

The key
The value

Syntax

Map <Key_type, value_type>

Example

void main() { 
   Map <String,String>m={'name':'Tom','Id':'E1001'}; 
   print('Map :${m}'); 
}

It should produce the following output −

Map :{name: Tom, Id: E1001}

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