Season’s Greetings, All,

I hope this holiday season finds each of you and your families in good health and good spirits. I tried to get this update out before Christmas, but it was not to be. I have several announcements (all positive) to make across several topics both near and far. I know everyone’s wondering what’s the deal with “Wave 2” given that it was supposed to have a release or some demos out this month and I will get to that in this post, I promise, but first I want to get a few quick but important asides out of the way.

Patreon Launch Update

First, let me say a gigantic THANK YOU! to everyone who responded to my call to action regarding my new Patreon. Thanks to your support I’m already well on the way to my first fundraising goal! I’m very pleased with the initial uptake and will be working on getting those tier rewards out ASAP. Every drop of support means the world to me in both a very practical way and in a psychological way. It really keeps the fight in me to know other folks still give a darn.

Also, got some part-time freelance VB contract work, one project of which is thanks to a Patreon supporter answering my call for opportunities. Working on VB projects is always a dream come true so thanks to that special supporter for this opportunity and for the rest of my supporters, please keep ’em coming!

“Wave 6” Theme Update

I wouldn’t normally concern you all with an update on something so far out but I wanted to give my readers some assurances that I have been paying attention to their pain points and am making plans to help. Originally, I didn’t have a clear vision on any specific themes after “Wave 5” (which is themed after LINQ). However, based on observation, a theme for “Wave 6” has emerged around C# interop. More specifically, I’ve seen a number of VB users being blocked by new APIs both in the .NET 6/7 profile and in 3^rd party libraries that use features such as the `unmanaged` constraint, stack-only “ref” structure types, and similar scenarios. Some cases where VB is being blocked, such as `required` members, are already being worked on by Microsoft and I sincerely thank them for it, but others they have announced no plans to address. I recognize the pain this causes VB users who are blocked from using these APIs and will be dedicating an entire milestone to designing and implementing some degree of support to unblock you, particularly with a focus on consuming these APIs and I wanted to share that intention with those impacted sooner rather than later. The wave plan is pretty fluid after “Wave 3” balancing several factors including the need for earlier design feedback but another factor is urgency so I may pull this new “Wave 6” in earlier. Stay tuned.

“Wave 2” Scope Update

“Wave 2” is all about unblocking new platforms through the repurposing of VB XML Literals syntax to enable declarative UI development on the web and cross-platform mobile development. This has always been the plan. What’s changed is that for a while now (years, in fact), I have been very cautious in describing the centerpiece feature of this wave as “Enhanced XML Literals”, “Target-Typed XML Literals”, “Pattern-based XML Literals”, or “a XAML-like syntax”, very intentionally avoiding the term “XAML Literals” because that term makes certain promises that I wasn’t willing to casually commit to. My intention was always to target a strategic subset of XAML syntax that would coincidentally produce the same result in common scenarios as what is used in Xamarin.Forms, but wouldn’t be bound to the full breadth of scenarios of a technology like WPF or the formal XAML specification. And for what I prototyped back in 2019 that was good enough.

What’s changed is the scope of technologies being targeted. WPF (and UWP) already support XAML design/code generation for VB.NET projects. The missing stories were ASP.NET Core for Web and Xamarin for Mobile. Xamarin.Forms (and by extension .NET MAUI) was designed to mimic the idioms of WPF but is implemented very differently in how those declarative idioms are translated to code. In places where WPF (and Silverlight) re-invented certain programming constructs in a distinct way from the .NET languages, Xamarin often embraces the “C#”-native way of implementing those idioms. For example, for control- and data-templating, WPF uses an arcane infrastructure behind the scenes using factories to instantiate controls, repeatedly in the case of `ItemsControls`, at runtime (deferred) given a declarative template written in XML. Xamarin.Forms on the other hand embraces lambda expressions. A lambda expression is the idiomatic way in C# (or VB or F#) for passing instructions to an object for how to construct something in a differed way that can then be called into over and over again. If you look at the constructor for the Xamarin.Forms DataTemplate class, it takes a Func(Of Object). WPF by contrast is not nearly so straightforward to use in an imperative code-only way.

Because I only needed to go after Xamarin.Forms, my design for the factory patterns an XML Literal would translate into were pretty narrowly targeted at what would unblock declarative Xamarin.Forms capabilities in VB with only loose consideration of what kinds of patterns would be necessary to target non-trivial WPF expressions.

With all that said, the scope of technologies I’m now pursuing has changed. I’m now targeting:

• ASP.NET Core
• Blazor
• Xamarin.Forms/.NET MAUI
• Avalonia UI
• possibly OpenSilver
• other technologies

To be clear, though this might smell like “scope creep” as a language designer this is a really good thing! Designing a feature around a broader set of scenarios generally yields better, more generalized features with greater applicability, which is generally preferable to the accumulation of one-offs.

All of these potential targets are being actively and holistically considered in the design and implementation of this feature. Avalonia UI is the critical addition to this list because unlike Xamarin.Forms it embraces a very WPF-like translation of declarative XAML into .NET objects. Additionally, in designing the patterns for translation I am acutely aware that 1) someone will have to write the “builder” libraries that enable support of a particular technology and their life shouldn’t be overly tedious (e.g. they shouldn’t need to explicitly code support for every dependency property or conversion in an entire framework), and 2) VB users will want to consume 3^rd party components written targeting these technologies that have no knowledge of this feature, or themselves may implement controls or user controls targeting those technologies and that I do not want to place a burden on those VB users to mediate integration of those components with the feature.

All of that has led me to the conclusion that I must embrace fully* the XAML-osity of the feature to provide the best experience for VB users. I’m effectively designing and implementing a XAML “meta-processor” inside the VB compiler—a feature that allows one to efficiently describe and implement multiple technology-specific XAML processors in a prescribed way. This design shift raises the bar significantly for the feature but it’s also very liberating in that I don’t need to employ as many workarounds to support certain scenarios in indirect ways. For example, markup extensions (e.g. {Binding}) until now were a concept I wanted to be completely opaque to the compiler with it passing enough information to the builder library that it could then parse and interpret those markup expressions at runtime. Or certain elements of the XAML language like x:Name, x:Type, and x:TypeArguments that are defined by XAML which before were meaningless to the compiler itself and very complicated to reproduce at runtime. Those are restrictions I placed on myself, but now these are things described by the formal XAML specification that the compiler can fairly know about.

I know some folks might find such deep integration of yet another language into the VB language/compiler distasteful and it’s absolutely not a coupling I take on lightly but over the last 14 years, time and time again new technologies have taking bets on the XAML language and I believe it is now stable enough, mature enough, and enduring enough to take a bet on too, not unlike the bet VB (and C#) both took on the SQL-like syntax of LINQ.

That said, even though I’ve fully* embraced “XAML Literals” as the north star of the feature I still put an asterisk on that word “fully” because I want to be clear that I’m still very consciously constraining myself on the minimal integration of concepts absolutely mandated by the XAML spec (with which I’m now becoming intimately familiar) and required to support these targeted platforms. I fully believe that “limitations foster creativity”. Accordingly:

Examples of things I’m ok with the language having some awareness of now:

• The basic conventions of XAML with regard to object creation and member setting (including “attached” properties and events).
• Things in the x: (xaml) namespace.
• That an attribute value represents a markup extension.

Examples of things I’m NOT ok with the language having any awareness of:

• Any particular technology or assembly names.
• Any particular technology namespaces.
• Any particular type specific to any particular technology (e.g. FrameworkElement, MarkupExtension, ContentPropertyAttribute, DependencyObject/DepedencyProperty).
• Type converters

I’m holding the line on the latter list, which means building the necessary layers of indirection for those scenarios. Every concept the language understands must be very carefully considered, even with this bold new shift. For example, I don’t want VB to “know” about type converters. It’s OK for a builder library to know about them but not for the language to know about them. They come with a lot of design baggage and raise questions I really don’t want to answer right now such as “Why do XAML literals understand and use type converters, but the basic casting syntax does not?” and that would be a fair question if the language or compiler did actually know about them. But as I am implementing them, these dependencies are properly hidden behind the abstraction of a XAML conversion without a direct requirement on how such a conversion is implemented. Further, such knowledge isn’t even hinted at by the XAML specification—the term type converter does not appear in the spec even once—this is an implementation detail coincidentally associated with WPF but not strictly mandated by the XAML language per se.

Oh, and FYI, here’s a picture of an Avalonia UI app running on Android built using VB!

So, yeah, in summary, they’re called XAML Literals now. I gave up (for the better).

XAML Literal Entanglements with “Wave 7”

OK, technically this isn’t an update because I never told anyone this to begin with but it’s impacting the schedule so I’m sharing to be a little more transparent. There’s a critical piece of the pattern of XAML Literals that was designed in a certain way that’s a little… special. But the plan was to have this specialness be a subset of some specialness that I’d expand on more in “Wave 3” with an otherwise unrelated feature. This matters cause if you do a thing once in a language it’s a one-off, but if you do it two or three times it’s a design pattern and that’s legit so that plan was to do both things the same way and introduce a new pattern.

The problem is that the feature in “Wave 3” also needed to be reconciled design-wise with the existence of source generators—a feature of both the VB (and C#) compilers that Microsoft introduced “recently”. UI frameworks are squarely in the set of core scenarios for source generation and the democratization of source generation should make any language designer consider very careful what goes in the language and what goes in a generator. Until recently I’d written a “TODO” to reconcile new features with source generation with a note that some of the stuff in waves “2” and “3” could change drastically or disappear once I took a serious look at source generation “in the future”. The idea of presenting to you all a design in “Wave 3” which could be obviated entirely by source generators just kept nagging at me so this month I took the time to seriously think through how the mysterious feature in “Wave 3” and source generation would co-exist in one sensible experience and the short of it is that the entire design of the feature in “Wave 3” was obliterated. The design made a lot of sense before source generators were shipped (I’d started designing it at a time when source generators seemed very complicated and unlikely to release) and with them having released, putting some serious design thought into it caused me to throw away … everything other than the end-developer experience I’m holding to, though the implementation will be completely different.

This design sidebar crystalized to me that the theme behind “Wave 7” would be exploring the impact of source generation on language design further. The feature tentatively in “Wave 3” might just move back to “Wave 7”. “Wave 7” might move up. And the piece of design shared between XAML Literals and the feature in “Wave 3” either becomes a strange one-off in the language or needs to be changed. So, I’m changing it to align with the design pattern I now anticipate using elsewhere in the language. It’s coming along well. It simplifies the design, actually. It’s not nearly as “clever” as it was before which is a surprisingly hard to let go of for some reason, but ultimately better for everyone else but my ego. As part of doing things The Right Way™ for ModVB, I strive to never ship an implementation which I can’t say in good faith is expected to be a durable design or implementation. Prototype code is meant to be throw-away, what ships in ModVB is not.

Conclusion

“Wave 2” did not and will not release in December 2022 as planned due to valuable design changes, namely: targeting Avalonia UI to enable cross-platform UI development in VB for Windows, MacOS, Linux, Android, iOS, and the web; embracing the XAML specification as a first-class goal; and the integration of forward-looking design intentions from “Wave 3” and what is now coalescing as “Wave 7”. Implementation is otherwise going well and the deliverables for “Wave 2” are now expected in January 2023. I promise that I believe these changes were the right and necessary decisions to make given the information at hand and look forward to showcasing the fruits of all this labor early in 2023.

I thank everyone for their continue patience and support and wish everyone continued Happy Holidays and a very Happy New Year!

Regards,

-ADG