verify 1.0.0

Validations made simple. An extension based validation DSL.

Validations made simple

A fp inspired validation DSL. For Dart and Flutter projects.

Requirements

The implementation of Verify relies heavily on dart extension methods, which are available for Dart versions >= 2.6

Features

• Completely extensible (create your own combinators, validator primatives, etc)
• Flexible Verify is an extension based API (There is not single class created its all pure functions)
• Customizable (Define you own error types) organize validators how ever you want
• Plays well with bloc

Usage

Creating validators

A Validator is just a simple function alias:

// S is the input type and T the output type
typedef Validator<S, T> = Either<List<ValidationError>, T> Function(S subject);

So you can create your own validator by just specifying a function for exmple:

final Validator_<String> emailValidator = (String email) {
  return email.contains('@') ? Right(email) : Left(Error('must contain @'))
}; 

Create simple validators from predicates

A simpler way is to use some of the built it helpers.

final contains@ = Verify.property(
  (String email) => email.contains('@'),
    error: Error('email has to contain @')
    );

final notEmpty = Verify.property<String>((str) => !str.isEmpty, error: Error('field required'));

Reuse validators

Use composition to build up more complex validators.

final Validator_<String> emailValidator = Verify.all([ contains@, notEmpty ])

Validate and transform

Validators are also capable of transforming their input, so for instance we can do parsing and validation in one go.

final Validator<String, int> intParsingValidator = (String str) => Right(int.parse(str));

final validator = intParsingValidator.onException((_) => Error('not an integer'));

Field validations

Given a model, for instance a user:

class User extends Equatable {
  final String phone;
  final String mail;
  final int age;

  User(this.phone, this.mail, this.age);

  @override
  List<Object> get props => [phone, mail, age];
}

Additional checks can be performed on the object and its fields using check and checkField

final userValidator = Verify.empty<User>()
    .check((user) => !user.phone.isEmpty, error: Error('phone empty'))
    .checkField((user) => user.mail, emailValidator);

final someUser = User('','', 25);
final Either<List<Error>, User> validationResult = userValidator.verify(someUser);

Built it validators

Verify doesn't come with many built it validators because the idea is to leave this to client code.

But it does have a few conviniences:

    final validator = RegExp(r"(^\d+$)") // Validator<String, int>
        .matchOr(Error('not just digits'))
        .map((str) => int.tryParse(str));