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.

Why Use typedef?

• Enhances Readability: Simplifies complex function types for easier understanding.
• Promotes Reusability: Facilitates the definition of versatile function signatures.
• Type-Safe Parameter Passing: Allows for clean and safe function parameterization.
• Ideal for Callbacks: Perfect for working with callbacks, event handlers, and functional programming patterns.

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

Using typedef

Example: 

// 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.

Using typedef as a parameter of a function

Example:

// 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 !!

Note: typedefs were restricted to function types before the 2.13 version of Dart

Typedef for Variables and Collections

Typedef is not restricted to functions; we can use variables and collections. Let us check the syntax for this:

typedef name = Collection;

Example:

// 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]

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Article Tags :

• Dart
• Dart Function