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. In this article, we will learn about Typedef in Dart.
How to Use Typedef with Dart Functions?
There are a few cases that tell us how to use typedef in Dart. Cases are mentioned below:
1. When we use typedef we can define the parameters of the function.
typedef function_name ( parameters );
2. With the help of typedef, we can also assign a variable to a function.
typedef variable_name = function_name;
3. After assigning the variable, if we have to invoke it then we go as:
variable_name( parameters );
By this we will be able to use a single function in different ways:
Programs to Illustrate the use of typedef
Example 1: Using typedef in Dart.
// Dart program to show the usage of typedef
// Defining alias name
typedef w3wiki(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 ${a + b}.");
}
// Main Function
void main() {
// Using alias name to define
// number with Geek1 function
w3wiki number = Geek1;
// Calling number
number(1, 2);
// Redefining number
// with Geek2 function
number = Geek2;
// Calling number
number(3, 4);
}
Output:
This is Geek1
1 and 2 are lucky geek numbers !!
This is Geek2
3 + 4 is equal to 7.
Note: Apart from this, typedef can also act as parameters of a function.
Example 2: Using typedef as a parameter of a function.
// Dart program to show the usage of typedef
// Defining alias name
typedef w3wiki(int a, int b);
// Defining Geek1 function
Geek1(int a, int b) {
print("This is Geek1");
print("$a and $b are lucky geek numbers !!");
}
// Defining a function with a typedef variable
number(int a, int b, w3wiki geek) {
print("Welcome to w3wiki");
geek(a, b);
}
// Main Function
void main() {
// Calling number function
number(21, 23, Geek1);
}
Output:
Welcome to w3wiki
This is Geek1
21 and 23 are lucky geek numbers !!
Note: typedefs were restricted to function types before the 2.13 version of Dart
Typedef for Variable and Collections
Typedef is not restricted to functions we can use variables and collections. Let us check syntax for this:
typedef name = Collection;
Below is the Example for Collection is mentioned below:
// Dart program to show the usage of typedef
// Defining alias name
typedef List_Integer = List<int>;
// Main Function
void main() {
// Using alias name to Declare
// List of Integer type
List_Integer x=[11,21,31];
// Print the List
print(x);
}
Output:
[11 , 21, 31]