[Proposal] Rename `Microsoft.UI.Reactor` to `Microsoft.UI.Declarative`

[ethanparker436]

Problem

The term Reactor may not immediately communicate the framework's purpose to developers encountering the project for the first time.

In the WinUI ecosystem, technologies are often identified by names that closely reflect their primary programming model or implementation approach. For example:

• Repository: microsoft-ui-xaml
• Namespace: Microsoft.UI.Xaml

A developer can immediately infer that the technology is centered around XAML.

By comparison, the name Reactor does not provide a similar level of clarity. A new developer evaluating the project may not understand what it offers without reading the documentation, whereas the framework's primary differentiator is that it provides a declarative, component-based way to build WinUI applications.

Since the project is still experimental and expected to evolve, this may be an opportunity to evaluate whether the current naming best supports discoverability and onboarding.

Proposed solution

Consider renaming the repository and namespace from Reactor to Declarative, emphasizing the framework's primary programming model.

Examples:

• Repository: microsoft-ui-declarative
• Namespace: Microsoft.UI.Declarative

This would align the naming more closely with the way WinUI technologies are commonly presented and make the framework's purpose more obvious to first-time users.

Alternatives considered

If a full project rename is considered too disruptive, an alternative option could be keeping the project name as Reactor while renaming only the namespace to Microsoft.UI.Declarative.

Additional context

The project README currently describes Reactor as:

"A declarative, component-based C# framework for building WinUI 3 desktop apps."

Because the declarative programming model is one of the project's primary differentiators, a name that directly reflects that characteristic may improve discoverability and reduce the amount of explanation required for new users.

The project is currently marked as experimental, which may make this the least disruptive stage at which to evaluate naming changes if they are considered beneficial.

Confirmation

• I have searched existing issues and specs for prior discussion of this idea.

[codemonkeychris]

Yeah, "Reactor" as a name won't survive, +1 to coming up with a new name.

Declarative - I think of XAML as declarative, I know that a lot of folks refer to functional programming as declarative, so I get that term.

Functional - I think that's also a good root, however, Reactor doesn't require you to write functional C#. You can build the graph using classic OOP and imperative C#. I wouldn't want to dissuade people from using the lib because of the name.

MVU - Very geeky name, but also pretty descriptive of what it's offering.

Other ideas? Let's brainstorm as many ideas as we can come up with and see what feels best!

[mdtauk]

As it is tied to WinUI (in this repo at least) using the succinct C# UI is too broad. (unless there was a standard language level approach, and you have WPF, WinUI, MAUI flavours)

WinUI Direct was something I had postulated on, but that may cause a confusion with XamlDirect.
WinUI Declare would slip off the tounge better than Declarative.
WinUI Component would be truer to the way it functions.
Win SharpUI if it remains C# only - but I think WinUI being C code under the hood this feel disingenuous.

Microsoft already has products with DirectUI as a name, and previously had Iris.

jetpack Compose - Composition and Composables
SwiftUI has Views (but Swift and SwiftUI are nicer names)

[Hefaistos68]

Microsoft.UI.coded maybe? Anything is better than Reactor I guess.

[lextm]

@Hefaistos68 Coded UI was once an automated testing framework from Microsoft, so Microsoft.UI.Coded remains ambiguous.

[Hefaistos68]

Microsoft.UI.Coded remains ambiguous.

That never stopped MS - see M365 Copilot and GH Copilot 🤣

[ethanparker436]

Reviewing the situation, I've actually had a change of heart and think we should keep the name "Reactor". Here is why:

The Rust ecosystem is notorious for its struggle with native GUI frameworks, where developers are often forced to rely on WebViews that just render HTML. However, thanks to Reactor, bindings were created through the windows-reactor crate, making it truly possible to use WinUI 3 natively and seamlessly for the first time.

The windows-reactor crate has been a massive success, and many developers are actively engaging with the microsoft/windows-rs repository because of it (just look at the recently opened and closed issues). Changing the name now would cause unnecessary confusion in the Rust community, where "Reactor" is already becoming established.

Furthermore, the name "Reactor" isn't inherently bad; it just doesn't explicitly describe the framework's underlying mechanics, which is perfectly fine for a proper noun.

@kennykerr @riverar, what are your thoughts on this? Given your work on the Windows ecosystem for Rust, your perspective would be incredibly valuable here.

[kennykerr]

I don't see the windows-reactor crate name changing, but Rust has a different philosophy on naming where short and memorable names are preferred. So reactor and canvas work well. The windows- prefix is just a convention I've adopted for the windows-rs family of crates to disambiguate. Other popular examples include serde, quote, syn, anyhow, nom, hashbrown, and so on.

And yes as @ethanparker436 points out, there's been a great deal of interest and early adoption already so there would need to be a good reason to switch the name at this point. Naturally, .NET has a different naming philosophy so the two projects don't need to share a name but that does help with recognition.

[saint4eva]

Reactor is still the best option here - no need to change it. Remember when they wanted to change Roslyn name, but they ended keeping Roslyn because it is better. Flutter or Jetpack does not really mean anything at first, but when people started using it, it became something. So, WinUI Reactor is great for WinUI, as Maui Reactor is great for .NET Maui. It is all about MVU pattern. Moreover , Declarative is very broad and means so many things. A new comer will read the docs and understand what WinUI Reactor is all about and its purpose.

[riverar]

Not sure the original microsoft-ui-xaml name is an example of great naming given it houses WinUI 2.x (in the Windows namespace) and 3.x (in the Microsoft namespace) and can be used without writing a single line of "XAML". 😂

[tusharsnx]

I don't have a good naming suggestion, but I do want to point out that the name should be short, and single-worded so it can serve its basic purpose which is to be able to get to the right documentations without needing a sophisticated search term. For example, I you can't even explain to me what you need to write modern windows apps using C++ in a single word.

Reactor seems to do that one thing right.

If Reactor's Rust and .Net designs are likely to diverge, I'd recommend having different names just to avoid the confusion between the two communities. Although they are built on a common foundation, WinUI, they are really two different frameworks following two different ways of handling projects/package management/auditing/testing/design, so it just makes sense to have different names.