How does this compare to other polyfills?

[slang25]

I like the look of this, and I've been eyeing up the prominent polyfills in the C# space at the moment, the main ones I'm aware being:

• PolySharp
• Polyfill
• PolyShim (this one)
  ... and there is another good one that I can't place at the moment. This package may be been created for your purpose and/or alternative to the above options, I was just wondering if you had a summary pitch about how the approach in this library compares to the listed alternatives.

[Tyrrrz]

Hi @slang25.

All of these libraries more or less do the same thing, but have slightly different design philosophies.

PolySharp was the first of the three libraries. It uses a source generator to provide polyfills, which in theory could be really powerful (i.e., trimming out polyfills that are not referenced by user code), but I'm not sure if Sergio did anything elaborate with that. It also originally started as polyfill library only for compiler plumbing code (mostly various attributes, IsExternalInit, and other stuff). I created a suggestion to expand that to also polyfill instance methods, but I think Sergio wasn't really found of the idea.

Then came Polyfill by Simon which was basically PolySharp with that suggestion being incorporated in the design. I think Simon experienced the same struggles as me, having to bridge gaps between various APIs in a bunch of projects, so he decided to build a library to do that. He chose against using the source generator approach and instead opted for a source-only package with code files that are imported during build. His library was the closest thing to what I needed, but I wanted to support really old .NET Framework versions (I have some .NET 3.5 projects for reasons) and he only plans to support .NET 4.6.1 and up.

Finally, I made PolyShim. It's more or less the same as Polyfill. The key differences are the following intentions:

• Support as wide range of frameworks as possible (.NET 3.5+). In some cases, you can get new APIs working on really decrepit frameworks.
• Polyfill as many types as possible. Simon's library relies on compatibility packages for things like ValueTuple<...>, Memory<T>, etc. My intention is to provide them all as well. This is because sometimes you may want to use one of those types internally without imposing dependencies on the upstream consumer.

Overall, even if you disregard the feature sets, at the end of the day all these libraries also differ in what kind of APIs they cover. It's pretty much impossible to provide a complete polyfill package, so I'm mainly focusing on things that I actually use in my projects and add new polyfills one at a time.

Hope that helps!

[Tyrrrz]

Also, here are some other polyfill libraries too! Just in case you didn't have too many options to consider already 😂

• https://github.com/JustArchiNET/Madness
• https://github.com/AgileObjects/NetStandardPolyfills
• https://github.com/theraot/Theraot
• https://github.com/OmerMor/AsyncBridge