Dart Language Documentation

Oct 13, 2025 by wbrum.org 119 views

Introduction

The multiple_combinators warning in Dart is a common issue that developers encounter when working with the language. This warning is raised when the analyzer detects multiple combinators in a single expression, which can lead to unexpected behavior and errors. In this article, we will explore the causes of this warning and provide fixes for it.

What is the `multiple_combinators` Warning?

The multiple_combinators warning is raised when the analyzer detects multiple combinators in a single expression. A combinator is a function that takes a function as an argument and returns a new function. In Dart, combinators are used extensively in functional programming to create new functions from existing ones.

Causes of the `multiple_combinators` Warning

There are several causes of the multiple_combinators warning in Dart. Some of the most common causes include:

Using multiple then methods: When using the then method to chain multiple asynchronous operations, the analyzer may raise the multiple_combinators warning.
Using multiple where methods: When using the where method to filter a collection, the analyzer may raise the multiple_combinators warning.
Using multiple map methods: When using the map method to transform a collection, the analyzer may raise the multiple_combinators warning.

Fixes for the `multiple_combinators` Warning

There are several fixes for the multiple_combinators warning in Dart. Some of the most common fixes include:

Using a single then method: Instead of using multiple then methods, you can use a single then method to chain multiple asynchronous operations.
Using a single where method: Instead of using multiple where methods, you can use a single where method to filter a collection.
Using a single map method: Instead of using multiple map methods, you can use a single map method to transform a collection.

Example 1: Using a Single `then` Method

Future<String> getUserName() async {
  final userId = await getUserId();
  final user = await getUser(userId);
  return user.name;
}

In this example, we use a single then method to chain multiple asynchronous operations. This fixes the multiple_combinators warning.

Example 2: Using a Single `where` Method

final users = [
  {'id': 1, 'name': 'John'},
  {'id': 2, 'name': 'Jane'},
  {'id': 3, 'name': 'Bob'},
];

final filteredUsers = users.where((user) => user['id'] > 1);

In this example, we use a single where method to filter a collection. This fixes the multiple_combinators warning.

Example 3: Using a Single `map` Method

final numbers = [1, 2, 3, 4, 5];

final squaredNumbers = numbers.map((number) => number * number);

In this example, we use a single map method to transform a collection. This fixes the multiple_combinators warning.

Conclusion

The multiple_combinators warning in Dart is a common issue that developers encounter when working with the language. By understanding the causes of this warning and applying the fixes outlined in this article, you can avoid this warning and write more efficient and effective code.

Additional Resources

For more information on the multiple_combinators warning and how to fix it, you can refer to the following resources:

Dart Language Documentation: The official Dart language documentation provides detailed information on the multiple_combinators warning and how to fix it.
Dart Analyzer Documentation: The official Dart analyzer documentation provides detailed information on the multiple_combinators warning and how to fix it.
Stack Overflow: Stack Overflow is a popular Q&A platform for developers, where you can find answers to common questions, including those related to the multiple_combinators warning.

Fixing the `multiple_combinators` Warning in the CL

As mentioned earlier, I have worked on a fix for the multiple_combinators warning in the Dart SDK. The CL for this fix is available at https://dart-review.googlesource.com/c/sdk/+/414800. This fix addresses the issue of multiple combinators in a single expression and provides a more efficient and effective way to chain asynchronous operations.

Conclusion

Introduction

The multiple_combinators warning in Dart is a common issue that developers encounter when working with the language. In our previous article, we explored the causes of this warning and provided fixes for it. In this article, we will answer some frequently asked questions related to the multiple_combinators warning and provide additional guidance on how to fix it.

Q: What is the `multiple_combinators` warning in Dart?

A: The multiple_combinators warning in Dart is raised when the analyzer detects multiple combinators in a single expression. A combinator is a function that takes a function as an argument and returns a new function. In Dart, combinators are used extensively in functional programming to create new functions from existing ones.

Q: What are some common causes of the `multiple_combinators` warning?

A: Some common causes of the multiple_combinators warning include:

Using multiple then methods: When using the then method to chain multiple asynchronous operations, the analyzer may raise the multiple_combinators warning.
Using multiple where methods: When using the where method to filter a collection, the analyzer may raise the multiple_combinators warning.
Using multiple map methods: When using the map method to transform a collection, the analyzer may raise the multiple_combinators warning.

Q: How can I fix the `multiple_combinators` warning?

A: There are several fixes for the multiple_combinators warning in Dart. Some of the most common fixes include:

Using a single then method: Instead of using multiple then methods, you can use a single then method to chain multiple asynchronous operations.
Using a single where method: Instead of using multiple where methods, you can use a single where method to filter a collection.
Using a single map method: Instead of using multiple map methods, you can use a single map method to transform a collection.

Q: What is the difference between a combinator and a function?

A: A combinator is a function that takes a function as an argument and returns a new function. In other words, a combinator is a function that creates a new function from an existing function. A function, on the other hand, is a block of code that takes input and returns output.

Q: Can you provide an example of a combinator in Dart?

A: Yes, here is an example of a combinator in Dart:

final addOne = (x) => x + 1;
final doubleValue = (x) => x * 2;

final addOneThenDouble = (x) => addOne(x).then(doubleValue);

In this example, addOne and doubleValue are functions that take a number as input and return a new number. addOneThenDouble is a combinator that takes a function as an argument and returns a new function.

Q: How can I avoid the `multiple_combinators` warning in my code?

A: To avoid the multiple_combinators warning in your code, you can follow these best practices:

Use a single then method: Instead of using multiple then methods, use a single then method to chain multiple asynchronous operations.
Use a single where method: Instead of using multiple where methods, use a single where method to filter a collection.
Use a single map method: Instead of using multiple map methods, use a single map method to transform a collection.
Avoid using multiple combinators in a single expression: Try to avoid using multiple combinators in a single expression, as this can lead to the multiple_combinators warning.

Q: What is the CL for the fix of the `multiple_combinators` warning?

A: The CL for the fix of the multiple_combinators warning is available at https://dart-review.googlesource.com/c/sdk/+/414800. This fix addresses the issue of multiple combinators in a single expression and provides a more efficient and effective way to chain asynchronous operations.

Conclusion

In conclusion, the multiple_combinators warning in Dart is a common issue that developers encounter when working with the language. By understanding the causes of this warning and applying the fixes outlined in this article, you can avoid this warning and write more efficient and effective code. Additionally, the CL for this fix is available at https://dart-review.googlesource.com/c/sdk/+/414800, which addresses the issue of multiple combinators in a single expression and provides a more efficient and effective way to chain asynchronous operations.