Supertypes is a library for generating complex records. This library has been heavily inspired by TypeScript's Utility Types.

Installation

Add supertypes and it's companion generator to your pubspec.yaml. The easiest way to do this is to use the command line:

For Dart projects:

dart pub add supertypes dev:supertypes_generator dev:build_runner

For Flutter projects:

flutter pub add supertypes dev:supertypes_generator dev:build_runner

To generate the types, run build_runner:

For Dart projects:

dart run build_runner build # Build once
dart run build_runner watch # Build continuously

For Flutter projects:

flutter pub run build_runner build # Build once
flutter pub run build_runner watch # Build continuously

Usage

Every file containing a supertype must have the following:

It should start with a part directive.

import 'package:supertypes/supertypes.dart';

part 'example.supertypes.dart';

It should contain a typedef with the name of the supertype, prefixed with $ for public generated records, or _$ for private generated records.

// Generates a public record called `Example`
@superType
typedef $Example = ();

// Generates a private record called `_Example`
@superType
typedef _$Example = ();

Index

• Modifier types
  • Partial
  • Required
  • Omit
    • Omitting positional fields
  • Pick
    • Picking positional fields
• Using Supertypes within another Supertype

Modifier types

Modifier types are types that take one or more types and return a new type.

Partial

The Partial modifier type takes a type and makes all of it's fields optional.

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

typedef Person = ({
  String firstName,
  String lastName,
  int age,
});

// We want to make all the field nullable to support partial updates
@superType
typedef $UpdatePerson = Partial<Person>;

// This generates:
typedef UpdatePerson = ({
  String? firstName,
  String? lastName,
  int? age,
});

Required

The Required modifier type takes a type and makes all of it's fields required.

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

// Let's say we have a person type with `lastName` nullable, 
// and we can't update the type easily. 
// We can instead create a new type with all fields required.
typedef Person = ({
  String firstName,
  String? lastName,
  int age,
});

// We want to make all the field nullable to support partial updates
@superType
typedef $CreatePerson = Required<Person>;

// This generates:
typedef CreatePerson = ({
  String firstName,
  String lastName,
  int age,
});

Omit

The Omit modifier type takes a type and a list of fields to omit from the type.

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

typedef Person = ({
  String firstName,
  String lastName,
  int age,
});

// We want to remove age from the type
@superType
typedef $PersonWithoutAge = Omit<Person, ({Omit age})>;

// This generates:

/// Generate for [$PersonWithoutAge]
typedef PersonWithoutAge = ({
  String firstName,
  String lastName,
});

Omitting positional fields

It's possible to also omit a positional field. For example:

typedef Person = (String name, int age);

// We want to remove the x field from the type
@superType
typedef $Age = Omit<Person, (Omit,)>; // This removes the first positional field

// This removes the second positional field. 
// We use `Pick` as a placeholder for the first positional field.
@superType
typedef $Name = Omit<Person, (Pick, Omit)>; 

// This generates:

/// Generate for [$Age]
typedef Age = (int,);

/// Generate for [$Name]
typedef Name = (String,);

Pick

The Pick modifier type takes a type and a list of fields to pick from the type and ignores the rest.

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

typedef Person = ({
  String firstName,
  String lastName,
  int age,
});

// We want to remove age from the type
@superType
typedef $PersonWithoutAge = Pick<Person, ({Pick firstName, Pick lastName})>;

// This generates:

/// Generate for [$PersonWithoutAge]
typedef PersonWithoutAge = ({
  String firstName,
  String lastName,
});

You can also apply a modifier type to the fields you pick:

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

typedef Person = ({
  String? firstName,
  String? lastName,
  int age,
});

// Let's make age nullable and and pick firstName as a required field
@superType
typedef $PersonWithNullableAge = Pick<Person, ({Required firstName, Partial age})>;

// This generates:

/// Generate for [$PersonWithNullableAge]
typedef PersonWithNullableAge = ({
  int? age,
  String firstName,
});

Picking positional fields

It's possible to also pick a positional field. For example:

typedef Person = (String name, int age);

// We want to remove the x field from the type
@superType
typedef $Name = Pick<Person, (Pick,)>; // This removes the first positional field

// This removes the second positional field. 
// We use `Pick` as a placeholder for the first positional field.
@superType
typedef $Age = Pick<Person, (Omit, Pick)>; 

// This generates:

/// Generate for [$Name]
typedef Name = (String,);

/// Generate for [$Age]
typedef Age = (int,);

Using Supertypes within another Supertype

Supertypes can be used within other supertypes. This is useful for creating complex types that can be reused. To use a supertype within another supertype, simply use the original type you prefixed with $ or _$.

import 'package:supertypes/supertypes.dart';

part 'person.supertypes.dart';

typedef Person = ({
  String firstName,
  String lastName,
  int age,
});

@superType
typedef $CreatePerson = Required<Person>;

@superType
typedef $UpdatePerson = Partial<Person>;

@superType
typedef $PersonOperation = ({
  $CreatePerson create,
  $UpdatePerson update,
});

// This generates:

/// Generate for [$CreatePerson]
typedef CreatePerson = ({
  int age,
  String firstName,
  String lastName,
});

/// Generate for [$UpdatePerson]
typedef UpdatePerson = ({
  int? age,
  String? firstName,
  String? lastName,
});

/// Generate for [$PersonOperation]
typedef PersonOperation = ({
  ({
    int age,
    String firstName,
    String lastName,
  }) create,
  ({
    int? age,
    String? firstName,
    String? lastName,
  }) update,
});

Features:

• More modifier types
  • ✅ Partial - Make all fields nullable
  • ✅ Required - Make all fields required
  • ✅ Omit - Omit fields from a type
  • ✅ Pick - Pick fields from a type
  • Merge - Merge two types
  • WithRequired - Make certain fields required
  • WithPartial - Make certain fields optional
  • Awaited - Unwrap a Future type recursively
• JSON serialization and deserialization for records
  • Generate fromJson top level function
  • Generate toJson extension method on the record
• Support for using classes in the supertype records by extracting their fields