Either class of dartz library

Ayushi Agarwal

29 April 2023

Either class of dartz library is used to return two type of data from a single function.

Suppose, there is an method which convert input String value in int and return it.

int convertVal(String data) {
    return num.parse(data);
  }

int convertVal(String data) {

return num.parse(data);

}

Here, we can only return a int value. If we get any error and handle it in our code, still we will have to return int value only. We are not able to send error message in this case.

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Either class

If we wanna return two type of data, we can use Either class of dartz library. For this, we need to add dartz library in our project.

In above example, we can return int value as successful result and error message in failure case.

Implementation

Step 1 : Add dependency

dartz: ^0.8.9

1	dartz: ^0.8.9

NOTE : To check latest package & learn more about dartz package, check following link : dartz

Step 2 : Function implementation

Import following package :

import 'package:dartz/dartz.dart';

1	import 'package:dartz/dartz.dart';

Now, wrap data which we wanna return, in Left & Right class and return them.

Either<String, int> convertVal(String data) {
    try {
      return Right(num.parse(data));
    } catch(e) {
      return Left(e.toString());
    }
  }

Either<String, int> convertVal(String data) {

try {

return Right(num.parse(data));

} catch(e) {

return Left(e.toString());

}

NOTE : Here, we wrap success result in Right class and failure result in Left class. You can change them. Also, you can wrap any object class as well.

Step 3 : Handle result

var result = convertVal("AA33"); // pass any integer or non-integer value
              result.fold(
                      (l) {   // if there is any error, this block will execute   
                        print("Error: "+l);
                      },
                      (r) {   // if we get successful result, this block will execute 
                        print(r);
                      });

var result = convertVal("AA33"); // pass any integer or non-integer value

result.fold(

(l) { // if there is any error, this block will execute

print("Error: "+l);

(r) { // if we get successful result, this block will execute

print(r);

});

Through fold method, we can handle result. For more methods of Either class, please check following link : Class-methods

You can check following link to check more blog related to flutter & dart : Blog

Hope, this blog will be helpful to you.