condition_builder

A Dart package for building and evaluating conditional logic chains in a fluent and readable way, with support for both synchronous and asynchronous operations.

✨ Features

  • Fluent API: Define conditional logic using a clear, chainable builder syntax (.on(...).orElse(...)).
  • Synchronous Builder: Easily handle synchronous conditions and return synchronous values.
  • Asynchronous Builder: Seamlessly work with Future-based conditions and return Future values.
  • Conditional Inclusion: Use .onIf(...) to include or exclude conditions based on other runtime boolean values.
  • Lazy Evaluation: Conditions and their associated values are evaluated only when the .build() method is called and only for the first condition that is met.
  • Clear Structure: Improves readability and maintainability compared to complex nested if-else statements for multi-way branching.

🚀 Installation

Add this to your package's pubspec.yaml file:

dependencies:
  condition_builder: <latest_version>

Then, run flutter pub get to install the package.

🏗️ Usage Example

String determineWeatherDescription(int temperature) {
  return ConditionBuilder<String>()
      .on(() => temperature < 0, () => "It's freezing!")
      .on(() => temperature >= 0 && temperature < 10, () => "It's cold.")
      .onIf(
        () =>
          DateTime.now().month > 5 &&
          DateTime.now().month < 9, // Only add 'pleasant' in summer months
        () => temperature >= 10 && temperature < 25,
        () => "It's a pleasant warm day.",
      )
      .onIf(
        () => temperature < 40, // If it's extremely hot, don't just say "It's hot."
        () => temperature >= 25,
        () => "It's hot!",
      )
      .orElse(() => "Temperature out of expected range.")
      .build()!; // Use ! if you are sure orElse will always be hit or you handle null
}

void main() {
  print(determineWeatherDescription(-5)); // Output: It's freezing!
  print(determineWeatherDescription(15)); // Output depends on the month
  print(determineWeatherDescription(30)); // Output: It's hot!
}

⚡ Asynchronous Example

For scenarios involving Future-based conditions or values (e.g., fetching data from an API, performing database operations, waiting for delays), use the AsyncConditionBuilder. It works similarly to the synchronous builder but handles asynchronous operations gracefully. The AsyncCondition class encapsulates a single asynchronous condition and its corresponding asynchronous value. When using the AsyncConditionBuilder, both the condition and value functions you provide to the .on(), .onIf(), and .orElse() methods must be marked with the async keyword and must return a Future.

The .build() method of AsyncConditionBuilder is also async and must be awaited when called. The builder will await each condition's evaluation in order until one returns true, then await its corresponding value function before returning the final Future result.

🤔 Why use this pattern?

This pattern is beneficial when you have:

  • Multiple distinct conditions that determine a single outcome value.

  • Conditions or values that require potentially expensive computations or asynchronous operations that should only run if necessary.

  • A desire to make complex conditional logic more readable and structured than complex nested if-else statements for multi-way branching.

  • A need to conditionally include or exclude entire conditions based on other factors at runtime.

🛠️ Contributing

Contributions are welcome! If you find bugs, improvements, or need new features, feel free to submit an issue or pull request.

📜 License

This project is licensed under the MIT License. Feel free to use and modify it as needed.

Libraries

condition_builder