dart-use-primary-constructors

Name: dart-use-primary-constructors
Author: flutter

788installs159forks

How to install dart-use-primary-constructors?

flutter/agent-plugins/dart-use-primary-constructors

$npx -y skills add flutter/agent-plugins --skill dart-use-primary-constructors

Installs into the current project.

Summary

Help users write syntactically and semantically correct primary constructors in Dart, and migrate/use the new constructor syntax, empty-body semicolon syntax, in-body initializer list syntax, and abbreviated concise constructor syntax.

Files · 1

View on GitHub

SKILL.md

1	# Dart Primary Constructors & New Constructor Syntax Skill
2
3	Use this skill when helping users write, refactor, or debug code using Dart's Primary Constructors feature.
4
5	### Dart Version Requirements
6	* Dart 3.13 and above: Primary constructors are enabled by default.
7	* Dart 3.12: The feature is available but experimental. Users must explicitly enable the experiment flag `primary-constructors` via `--enable-experiment=primary-constructors` or in `analysis_options.yaml`:
8	```yaml
9	analyzer:
10	enable-experiment:
11	- primary-constructors
12	```
13	* Dart 3.11 and earlier: Primary constructors are not supported.
14
15	---
16
17	## 1. Overview
18	Primary Constructors allow developers to declare a non-redirecting generative constructor as well as a set of instance variables directly in the class header. This significantly reduces boilerplate and improves code readability.
19
20	### Key Benefits
21	- Combines field declaration, parameter declaration, and initialization into a single declaration known as a declaring parameter declaration.
22	- Enables safe reference to constructor parameters in non-late field initializers (Primary Initializer Scope).
23	- Allows empty declaration bodies to be represented concisely with a semicolon (`;`).
24	- Introduces abbreviated concise syntax for in-body constructors.
25
26	---
27
28	## 2. Syntax Reference
29
30	### 2.1 Basic Class Header Syntax
31	To declare a primary constructor, place a parameter list immediately after the type name (and optional type parameters):
32
33	```dart
34	// Declares fields x and y, and a generative constructor Point(this.x, this.y)
35	class Point(var int x, var int y);
36
37	// Declares final fields
38	class PointFinal(final int x, final int y);
39	```
40
41	### 2.2 Declaring, Initializing, and Plain Parameters
42	A primary constructor parameter list distinguishes between three types of parameters:
43	1. Declaring Parameters: Indicated by the `var` or `final` modifier (e.g., `final int x`). They implicitly create a corresponding instance field in the class.
44	2. Initializing Parameters: Indicated by the `this.` or `super.` prefix (e.g., `this.x` or `super.x`). They initialize an existing field or a super constructor parameter, respectively.
45	3. Regular Parameters: Declared without modifiers (e.g., `int y`). They do not become fields and are only available during initialization (e.g., in field initializers or the `this :` initializer list in the class body).
46
47	```dart
48	// `x` is a field and a parameter because it has the keyword `final`. In particular, we can use the name `x` in the initializer list in the in-body part of the primary constructor. 'y' is a only parameter because it has neither of the keywords `final` or `var`, but `y` is passed to the super constructor via the `this :` initializer list.
49	class C(final int x, int y) extends Base {
50	this : super(y);
51	}
52	```
53
54	Declaring parameters and initializing parameters are two ways of achieving the same goal: declaring a class with instance fields which are set in the constructor. Regular parameters are different in that their values are not automatically routed to an instance field.
55
56	### 2.3 Constant Primary Constructors
57	To make a primary constructor `const`, place the `const` keyword before the class/type name in the declaration header:
58
59	```dart
60	class const Point(final int x, final int y);
61	extension type const Ext(int x);
62	enum const MyEnum(final int x) {
63	entry(1);
64	}
65	```
66
67	### 2.4 Extension Types
68	Extension types must use primary constructors.
69	- The single parameter in the header is the representation field.
70	- The representation variable cannot use the `var` modifier (using `var` triggers the `representation_field_modifier` error).
71	- The representation variable can optionally use the `final` modifier. If `final` is not present then it is inferred; that is, the parameter is declaring whether or not it's explicitly `final`.
72
73	### 2.5 Empty Body Semicolon Shorthand (`;`)
74	When a class, mixin class, mixin, extension or extension type has an empty body, the `{}` braces can be replaced by a semicolon (`;`):
75
76	```dart
77	class C(int x);
78	mixin class MC;
79	extension type ET(int x);
80	mixin M;
81	extension Ext on C;
82	```
83
84	### 2.6 The In-Body Part of a Primary Constructor (`this ...`)
85	If a primary constructor requires assertions or custom field initializations, they can be declared in the body using the `this :` syntax:
86
87	```dart
88	class Point(var int x, var int y) {
89	// Initializer list in class body
90	this : assert(x >= 0), y = y * 2;
91	}
92	```
93
94	You can also write a constructor body with this syntax (`this {...}`).
95
96	### 2.7 Abbreviated Concise Constructor Syntax
97	For constructors declared within t

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dart-use-primary-constructors

788installs159forks

View on GitHub

How to install dart-use-primary-constructors?

flutter/agent-plugins/dart-use-primary-constructors

$npx -y skills add flutter/agent-plugins --skill dart-use-primary-constructors

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Dart Primary Constructors & New Constructor Syntax Skill
2
3	Use this skill when helping users write, refactor, or debug code using Dart's Primary Constructors feature.
4
5	### Dart Version Requirements
6	* Dart 3.13 and above: Primary constructors are enabled by default.
7	* Dart 3.12: The feature is available but experimental. Users must explicitly enable the experiment flag `primary-constructors` via `--enable-experiment=primary-constructors` or in `analysis_options.yaml`:
8	```yaml
9	analyzer:
10	enable-experiment:
11	- primary-constructors
12	```
13	* Dart 3.11 and earlier: Primary constructors are not supported.
14
15	---
16
17	## 1. Overview
18	Primary Constructors allow developers to declare a non-redirecting generative constructor as well as a set of instance variables directly in the class header. This significantly reduces boilerplate and improves code readability.
19
20	### Key Benefits
21	- Combines field declaration, parameter declaration, and initialization into a single declaration known as a declaring parameter declaration.
22	- Enables safe reference to constructor parameters in non-late field initializers (Primary Initializer Scope).
23	- Allows empty declaration bodies to be represented concisely with a semicolon (`;`).
24	- Introduces abbreviated concise syntax for in-body constructors.
25
26	---
27
28	## 2. Syntax Reference
29
30	### 2.1 Basic Class Header Syntax
31	To declare a primary constructor, place a parameter list immediately after the type name (and optional type parameters):
32
33	```dart
34	// Declares fields x and y, and a generative constructor Point(this.x, this.y)
35	class Point(var int x, var int y);
36
37	// Declares final fields
38	class PointFinal(final int x, final int y);
39	```
40
41	### 2.2 Declaring, Initializing, and Plain Parameters
42	A primary constructor parameter list distinguishes between three types of parameters:
43	1. Declaring Parameters: Indicated by the `var` or `final` modifier (e.g., `final int x`). They implicitly create a corresponding instance field in the class.
44	2. Initializing Parameters: Indicated by the `this.` or `super.` prefix (e.g., `this.x` or `super.x`). They initialize an existing field or a super constructor parameter, respectively.
45	3. Regular Parameters: Declared without modifiers (e.g., `int y`). They do not become fields and are only available during initialization (e.g., in field initializers or the `this :` initializer list in the class body).
46
47	```dart
48	// `x` is a field and a parameter because it has the keyword `final`. In particular, we can use the name `x` in the initializer list in the in-body part of the primary constructor. 'y' is a only parameter because it has neither of the keywords `final` or `var`, but `y` is passed to the super constructor via the `this :` initializer list.
49	class C(final int x, int y) extends Base {
50	this : super(y);
51	}
52	```
53
54	Declaring parameters and initializing parameters are two ways of achieving the same goal: declaring a class with instance fields which are set in the constructor. Regular parameters are different in that their values are not automatically routed to an instance field.
55
56	### 2.3 Constant Primary Constructors
57	To make a primary constructor `const`, place the `const` keyword before the class/type name in the declaration header:
58
59	```dart
60	class const Point(final int x, final int y);
61	extension type const Ext(int x);
62	enum const MyEnum(final int x) {
63	entry(1);
64	}
65	```
66
67	### 2.4 Extension Types
68	Extension types must use primary constructors.
69	- The single parameter in the header is the representation field.
70	- The representation variable cannot use the `var` modifier (using `var` triggers the `representation_field_modifier` error).
71	- The representation variable can optionally use the `final` modifier. If `final` is not present then it is inferred; that is, the parameter is declaring whether or not it's explicitly `final`.
72
73	### 2.5 Empty Body Semicolon Shorthand (`;`)
74	When a class, mixin class, mixin, extension or extension type has an empty body, the `{}` braces can be replaced by a semicolon (`;`):
75
76	```dart
77	class C(int x);
78	mixin class MC;
79	extension type ET(int x);
80	mixin M;
81	extension Ext on C;
82	```
83
84	### 2.6 The In-Body Part of a Primary Constructor (`this ...`)
85	If a primary constructor requires assertions or custom field initializations, they can be declared in the body using the `this :` syntax:
86
87	```dart
88	class Point(var int x, var int y) {
89	// Initializer list in class body
90	this : assert(x >= 0), y = y * 2;
91	}
92	```
93
94	You can also write a constructor body with this syntax (`this {...}`).
95
96	### 2.7 Abbreviated Concise Constructor Syntax
97	For constructors declared within t

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