Callable Classes in Dart

Just like the functions, we can also call the instances of classes in Dart. Such classes are also known as “callable ” classes. We need to use the “call( )” function to implement the callable class.

Syntax :

class class_name 
{
String call( < arguments > )
{
// body of the function
// return statement 
}
main( )
{
    // calling the instance just like the functions
}

Example – 1 :

// definition of the callable class 
class Colour 
{  
  // definition of the call( ) function
  String call( String c_name, int hex_code ) 
    {  
        return( ' The colour name is $c_name and the hexdecimal code is $hex_code ' ) ; 
    }  
}  
void main( ) 
{  
   // creating the object of the class ' colour '
   Colour col = new Colour( ) ; 
   
   // calling the class instance just like a function
   var info = col( ' Black ', 002147 ) ;   
  
   // printing the information about the colour
   print( ' Dart Callable class ' ) ;  
   print( ' The information of the colour is : ' ) ;
  
   print( info ) ;  
}  

Output :

Dart Callable class 
 The information of the colour is : 
 The colour name is  Black  and the hexdecimal code is 2147

Explanation :

In this code, we defined a call( ) function with return type ‘ String ’ and two arguments of type ‘ String ’ and ‘ int ’ in the ‘ Colour ’ class.

This call( ) method accepts the value of the colour name and it hexadecimal value in the arguments and return the print statement. Then, in the main( ) function, an object ‘ col ’ of the class ‘ Colour ’ is created and the instance of the class call( ) is called just like a function.

var infro = col( ' Sharma ',18 ) ;       

Consider the following example in Dart that shows multiple callable classes

Example - 2 :

class Student 
{  
  String call( String name, int age ) 
  {  
      return( ' The student name is $name and the age is $age ' ) ;  
  }  
}  
class Teacher 
{  
  String call( String t_name ) 
  {  
      return( ' The name of the Teacher is : $t_name ' ) ;
  }  
}  
  
void main( ) 
{  
   Student stu = new Student( ) ;  
  
   Teacher tem = new Teacher( ) ;  
  
   // calling the instance of the class ' Student ' just like a function
   var s = stu( ' Yukta Malhotra ', 19 ) ; 
  
   // calling the instance of the class ' Teacher ' just like a function
   var t = tem( ' Dimple Chawla ' ) ;   


   print( ' Multiple Callable classes in Dart ' ) ;  
   
   print( s ) ;  
   print( t ) ;  
}  

Output :

Multiple Callable classes in Dart 
    The student name is  Yukta Malhotra  and the age is 19 
    The name of the Teacher is :  Dimple Chawla  

Explanation :

In the above code, we defined two callable functions in class ‘ Student ’ and class ‘ Teacher ’. The ‘ Student ’ class has ‘ call( ) ’ function that accepts two parameters of data types ‘ String ’ and ‘ int ’. The ‘ Teacher ’ class has a ‘ call( ) ’ function that accepts only one parameter of type ‘ String ’. We called instances of both the classes as callable functions.

var s = stu( ' Yukta Malhotra ', 19 ) ; 
   var t = tem( ' Dimple Chawla ' ) ;