Add 'Primary constructor' to glossary by sfshaza2 · Pull Request #13033 · flutter/website

sfshaza2 · 2026-02-04T22:18:27Z

Adds a definition for 'Primary constructor' to the glossary, focusing on its usage in Dart extension types.

gemini-code-assist · 2026-02-04T22:18:40Z

Summary of Changes

Hello @sfshaza2, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the project's documentation by introducing a new glossary term. The addition aims to clarify the concept of "Primary constructor," specifically highlighting its application within Dart's extension types, thereby improving the comprehensibility of related technical documentation.

Highlights

Glossary Enhancement: A new entry for "Primary constructor" has been added to the glossary.yml file, providing a detailed definition, short description, relevant links, and categorizing labels.

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Changelog

src/data/glossary.yml
- Added a new term 'Primary constructor' including its short and long descriptions, related external links to Dart documentation, and 'dart' and 'language' labels.

Activity

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Code Review

This pull request adds a definition for 'Primary constructor' to the glossary. The definition is good, but it's slightly outdated as it only mentions extension types. I've suggested an update to include primary constructors for classes, which were introduced in Dart 3.4, and to add a relevant documentation link.

gemini-code-assist · 2026-02-04T22:25:40Z

src/data/glossary.yml

+  long_description: |-
+    A _primary constructor_ is a concise way to declare a constructor
+    directly in the type declaration.
+
+    Currently, this feature is only available for [extension types][].
+    It allows you to define the underlying representation object
+    and bind it to a field in one step.
+
+    [extension types]: https://dart.dev/language/extension-types
+  related_links:
+    - text: "Extension types constructors"
+      link: "https://dart.dev/language/extension-types#constructors"
+      type: "external"


The description for primary constructors is slightly outdated. Since Dart 3.4, primary constructors are also available for classes, not just extension types.

I'd suggest updating the description to include classes and adding a link to the relevant documentation for class-based primary constructors to make the glossary entry more accurate and complete.

long_description: |- A _primary constructor_ is a concise way to declare a constructor directly in the type declaration. Primary constructors can be used with [classes][] and [extension types][]. For classes, they allow you to define fields and initialize them from constructor parameters in one step. For extension types, they allow you to define the underlying representation object and bind it to a field. [classes]: https://dart.dev/language/constructors#primary-constructors [extension types]: https://dart.dev/language/extension-types related_links: - text: "Primary constructors for classes" link: "https://dart.dev/language/constructors#primary-constructors" type: "external" - text: "Extension types constructors" link: "https://dart.dev/language/extension-types#constructors" type: "external"

'Dart 3.4' is not accurate, the new, generalized primary constructors feature hasn't yet been released, but it's being implemented and will definitely be released.

flutter-website-bot · 2026-02-04T22:26:05Z

Visit the preview URL for this PR (updated for commit 885f2ef):

https://flutter-docs-prod--pr13033-glossary-primary-constructo-qinhfcxj.web.app

kallentu · 2026-02-06T21:33:55Z

src/data/glossary.yml

@eernstg to review as well.

Thanks for the heads up!

I'll assume that this glossary entry should describe the primary constructors feature which is about to be released—it doesn't seem particularly useful to have one description of the concept for some weeks, and then updating it substantially to cover the much more general notion of primary constructors that we're about to release.

kallentu · 2026-02-06T21:36:24Z

src/data/glossary.yml

+    A _primary constructor_ is a concise way to declare a constructor
+    directly in the type declaration.
+
+    Currently, this feature is only available for [extension types][].


This is inaccurate -- primary constructors can be used for classes, extension types, and enums as well.

eernstg

Added a few comments.

Perhaps we should postpone landing this PR until the new primary constructors feature has been released?

eernstg · 2026-02-09T08:34:13Z

src/data/glossary.yml

Thanks for the heads up!

I'll assume that this glossary entry should describe the primary constructors feature which is about to be released—it doesn't seem particularly useful to have one description of the concept for some weeks, and then updating it substantially to cover the much more general notion of primary constructors that we're about to release.

eernstg · 2026-02-09T08:54:32Z

src/data/glossary.yml


+- term: "Primary constructor"
+  short_description: |-
+    A constructor declared as part of the type declaration.


The phrase 'type declaration' is rather vague. It's often used to designate a type annotation (as in "the variable has a type declaration" when talking about declarations like String s = '';), as well as the meaning which is intended here. It would be nice if we could use a phrase which is more precisely denoting a class declaration, a mixin class declaration, an enum declaration, or an extension type declaration.

Next, a class declaration starts at a keyword (often class, but we can also have final class, sealed class, and the like), and it ends at the final } of the class body (or, with the upcoming enhancements, a semicolon which is the entire class body on its own). This implies that every member declaration is also part of "the type declaration". The new thing is that the primary constructor is part of the header of the class declaration, it's not in the body.

Similarly for mixin class declarations etc.

Perhaps this would work:

Suggested change

A constructor declared as part of the type declaration.

A constructor declared in the header of a class or a similar type declaration.

eernstg · 2026-02-09T08:55:23Z

src/data/glossary.yml

+    A constructor declared as part of the type declaration.
+  long_description: |-
+    A _primary constructor_ is a concise way to declare a constructor
+    directly in the type declaration.


Suggested change

directly in the type declaration.

directly in the header of a class, mixin class, enum, or extension type declaration.

eernstg · 2026-02-09T09:08:47Z

src/data/glossary.yml

+    It allows you to define the underlying representation object
+    and bind it to a field in one step.


I think it's really great that this glossary entry is so short. It should allow developers to get to know about the concept of a primary constructor. There would be other pages about all the details.

So how do we communicate that the primary constructors of class, mixin class, and enum declarations have a large number of properties in common, and the primary constructors of extension types are different in several ways?

Here is one attempt at saying very little, but still enough to give the reader a relevant hint:

Suggested change

It allows you to define the underlying representation object

and bind it to a field in one step.

A primary constructor in a class, mixin class, or enum declaration is a concise

way to specify a constructor and a number of instance variables in a single

constructor declaration in the header.

A primary constructor in an extension type declaration allows you to define the

underlying representation variable and its type.

We can't even really say "in a single declaration" when it comes to extension types, because they don't support declaring the representation variable using a regular instance variable declaration in the first place. There is simply no other way to declare the representation variable (name and type) of an extension type than having a primary constructor.

eernstg · 2026-02-09T09:10:47Z

src/data/glossary.yml

+  long_description: |-
+    A _primary constructor_ is a concise way to declare a constructor
+    directly in the type declaration.
+
+    Currently, this feature is only available for [extension types][].
+    It allows you to define the underlying representation object
+    and bind it to a field in one step.
+
+    [extension types]: https://dart.dev/language/extension-types
+  related_links:
+    - text: "Extension types constructors"
+      link: "https://dart.dev/language/extension-types#constructors"
+      type: "external"


'Dart 3.4' is not accurate, the new, generalized primary constructors feature hasn't yet been released, but it's being implemented and will definitely be released.

Add 'Primary constructor' to glossary

885f2ef

sfshaza2 requested a review from a team as a code owner February 4, 2026 22:18

sfshaza2 requested review from conooi and mit-mit February 4, 2026 22:19

gemini-code-assist bot reviewed Feb 4, 2026

View reviewed changes

conooi requested a review from kallentu February 5, 2026 22:42

kallentu reviewed Feb 6, 2026

View reviewed changes

eernstg reviewed Feb 9, 2026

View reviewed changes

	A constructor declared as part of the type declaration.
	A constructor declared in the header of a class or a similar type declaration.

	directly in the type declaration.
	directly in the header of a class, mixin class, enum, or extension type declaration.

		It allows you to define the underlying representation object
		and bind it to a field in one step.

-    It allows you to define the underlying representation object
-    and bind it to a field in one step.
+    A primary constructor in a class, mixin class, or enum declaration is a concise
+    way to specify a constructor and a number of instance variables in a single
+    constructor declaration in the header.
+    A primary constructor in an extension type declaration allows you to define the
+    underlying representation variable and its type.

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sfshaza2 commented Feb 4, 2026

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