Typedef in Dart

Typedef in Dart is used to create a user-defined identity (alias) for a function, and we can use that identity in place of the function in the program code. When we use typedef we can define the parameters of the function.

Syntax: typedef function_name ( parameters );

With the help of typedef, we can also assign a variable to a function.

Syntax:typedef variable_name = function_name;

After assigning the variable, if we have to invoke it then we go as:

Syntax: variable_name( parameters );

By this we will be able to use a single function in different ways:

Example 1:  Using typedef in Dart.

Dart

// Dart program to show the usage of typedef

// Defining alias name
typedef GeeksForGeeks(int a, int b);

// Defining Geek1 function
Geek1(int a, int b) {
  print("This is Geek1");
  print("$a and $b are lucky geek numbers !!");
}

// Defining Geek2 function
Geek2(int a, int b) {
  print("This is Geek2");
  print("$a + $b is equal to ${a + b}.");
}

// Main Function
void main()
{
  // Using alias name to define
  // number with Geek1 function
    GeeksForGeeks number = Geek1;
  // Calling number
  number(1,2);

  // Redefining number
  // with Geek2 function
  number = Geek2;
  // Calling number
  number(3,4);
}

Output:

This is Geek1
1 and 2 are lucky geek numbers !!
This is Geek2
3 + 4 is equal to 7.

Note: Apart from this, typedef can also act as parameters of a function.

Example 2: Using typedef as a parameter of a function.

Dart

// Dart program to show the usage of typedef

// Defining alias name
typedef GeeksForGeeks(int a, int b);

// Defining Geek1 function
Geek1(int a, int b) {
  print("This is Geek1");
  print("$a and $b are lucky geek numbers !!");
}

// Defining a function with a typedef variable
number(int a, int b, GeeksForGeeks geek) {
  print("Welcome to GeeksForGeeks");
  geek(a, b);
}

// Main Function
void main()
{
  // Calling number function
  number(21,23, Geek1);
}

Output:

Welcome to GeeksForGeeks
This is Geek1
21 and 23 are lucky geek numbers !!