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Reflection is the least of the problems this solves.

The majority of the issues and gotchas listed in the generics FAQ for Java do not happen in C# at all. It is liberating.

Reflection is an advanced use case that some people use, but it is rare.

The lack of flourish in. NET overtime more to what happens when a company takes the reins of a stack and later stops working on it.

Microsoft for a while invested and designed JavaScript, Python and Ruby versions for .NET. But when conditions changed, there was no interest to keep the projects going. These are all observations from an outsider at the time the projects were defunded.

Because of the siloed approach to development at the time, and the lack of an external county around those efforts, bootstrapping a community to drive those on their own proved to be very hard. Ruby mostly died, Python is barely surviving.

The mood in the ecosystem went from "we can build these and speed them up" to "this is an ongoing cost, let us rather interop with the real implementations rather than find constant catch up".

Meanwhile, languages that Microsoft did not build did flourish, like PHP

This corporate phenomenon deserves a blog post on its own

> The lack of flourish in. NET overtime more to what happens when a company takes the reins of a stack and later stops working on it.

But couldn't .NET not being a good target for dynamic languages be one of the reasons to stop working on it?

I keep hearing that .NET is a good platform for other languages, but there doesn't seem to be much empirical evidence for it (at least in dynamic languages).

I don’t know about all that in all honesty. I’m not a language designer so I suppose I don’t care about the why. All I know is Java is really bad at fulfilling my generic typing needs. Pragmatism is really important for languages, because without it all you have is a complicated excuse for a bad user experience. It’s sort of like how if you were to optimize English by cutting out redundant letters and combining words instead of making new words, you basically end up with German, which many English speakers would agree is not as nice a language to look at. (Germans may disagree of course because they’re used to it.)

I understand your point, however people complaining about Java are complaining about the language instead of the platform and the platform has evolved to support multiple languages.

Scala, Kotlin, Clojure, Eta (Haskell), JRuby are the ones I care about and they've been flourishing.

I'm a pragmatic at heart btw, but pragmatism sometimes leads to ignorance. It's important to see what's available on the other side of the fence without bringing the preconceptions bag with you. Because you can then actually use the metaphorical "best tool for the job".

It's what I'm doing myself, or at least trying and .NET is without a doubt evolving in a direction I like. And I can also write entire paragraphs of what's better on .NET, I just don't find the generics reification to be one of those things.

Is the suggestion that those languages can't easily written on CLR? There's a direct, maintained (by the one-man-army that is https://github.com/dmiller) port of Clojure to the CLR:

https://github.com/clojure/clojure-clr

This means that C# could be ported to the JVM, doesn't it?

> As a matter of fact such reflection is only needed because languages like Java or C# have very weak static type systems, compared with other languages in the ML family. With an expressive type system, you never need reflection capabilities.

The implication here is that you never need runtime type checking, which clearly isn't the case in ML family languages. Sum types for example have an abstract representation that must be resolved at runtime (for pattern matching).

C# also doesn't need reflection to resolve types (other than through the virtual route - i.e. inherited method resolution), this is a core feature of the CLR though (via `callvirt` [1] if I remember right) and not a weakness of C#'s type-system. C# bakes the concrete generic types into the generated IL.

[1] https://docs.microsoft.com/en-us/dotnet/api/system.reflectio...

> Sum types for example have an abstract representation that must be resolved at runtime (for pattern matching).

Indeed, but that's plain tagging, which is basically an int and not the same thing.

"callvirt" is basically doing a virtual method lookup in a vtable. It's still at runtime, but we are talking about OOP polymorphism now and how late binding works. Languages with type classes don't need that either, but that's a separate discussion and note that I still like OOP.

> C# also doesn't need reflection to resolve types

No, the developers do, because the language is not expressive enough to express generic pieces of code without losing type info, so you need reflection for constraints (e.g. "new T" or "instanceOf" checks) and runtime guards for downcasting.

Classic example: express a "sum" function that works on any Array<A>.

And note that what F# is doing to solve this particular problem is a hack to workaround both the lack of higher kinded types and of type classes and that does not interoperate with C#, since it requires "inline functions" which are doing type erasure (and it's a big and ugly hack, speaking of ML, because inline functions are no longer values ;-)).

> C# bakes the concrete generic types into the generated IL.

Of course, but that too is part of the problem.

> No, the developers do, because the language is not expressive enough to express generic pieces of code without losing type info, so you need reflection for constraints (e.g. "new T" or "instanceOf" checks) and runtime guards for downcasting.

The type system is totally capable of it. The language doesn't make it easy, but the code below is essentially type-classes and class-instances if you squint. It's something the C# team are looking into now anyway, but the main point is the type system doesn't preclude it.

    public interface Newable<A>
    {
        T New();
    }

    public struct NewableThing : Newable<Thing>
    {
        Thing New() => new Thing();
    }

    public class Foo
    {
        public A Bar<NewableA, A>() where NewableA : struct, Newable<A> =>
            default(NewableA).New();
    }

> Classic example: express a "sum" function that works on any Array<A>.

    public interface Num<A>
    {
        A Zero();
        A Add(A x, A y);
    }

    public struct NumInt : Num<int>
    {
        int Zero() => 0;
        int Add(int x, int y) => x + y;
    }

    public struct NumFloat : Num<float>
    {
        float Zero() => 0;
        float Add(float x, float y) => x + y;
    }

    public static A Sum<NumA, A>(A[] xs) where NumA : struct, Num<A> =>
        xs.Fold(default(NumA).Zero(), (s, x) => default(NumA).Add(s, x));

    int sumInt = Sum<NumInt, int>(new [] {1,2,3,4});
    int sumFlt = Sum<NumFloat, float>(new [] {1.0,2.0,3.0,4.0});

> Of course, but that too is part of the problem.

That's a very hand wavey statement. It's the goal of all staticly typed compilers to resolve to concrete types at compile time. How is part of any problem? The CLR has the capability to generate new concrete types from generic types at runtime if required, but obviously tries to do as much of that work up front at compile time.

You seem to mix up C# and CLR. The CLR can do type erasure if you want. It has an entire runtime called DLR to handle this stuff. Did you even know that? Type erasure was the only way before C# 2.0 when generics where introduced. The CLR can run Java just fine, we used to have J# before Oracle killed it through legal means. It has nothing to do with CLR technical limitations. You can run any fully fledged dynamic language on the CLR such as Python. Where is the practical problem here?

Next, you can't say that C# has a "weak" type system. It is mainly a strongly and statically typed by design. There are elements of weak typing in C# such as the dynamic keyword, and all C# type safety features can be bypassed if desired. It seems you prefer "weak" to mean "poor" but that is your definition, not the generally accepted one.

Further, it is completely false to indicate something to the effect that C#/CLR can't let other languages flourish on the platform. The CLR stands for "Common Language Runtime" and can run any language you can imagine, including weakly typed languages. It is a plain old finite stack machine at heart. Unlike JVM, the CLR is an ECMA standard and anyone can implement it and .NET sources are not GPL licensed.

Scala used to be available on CLR, and the reason it is not supported is more political than technical. You are again trying to make a technical justification for a political decision. Besides, Scala still only runs on JDK 8 which is funny because Oracle JDK will need a commercial license from 2019 to get patches so you're forced to switch to OpenJDK or pay for a Scala runtime.

The Java community has talked about value types forever, we know that. Good luck unwinding that decision, it is not that easy.

The cost for unsafe hacks to let Scala and Haskell work had more to do about the fact that .NET was not cross platform at that time. That was not the ecosystem impetus for for having Scala run on JVM. It was more because Java as a language is aging and lacks innovation which is well recognized. The cross platform argument against the CLR is gone now, so there is little reason why we shouldn't be able to run Scala and Haskell on CLR instead if you are after those languages.

Also, the point about "forcing JVM engineers to get creative" is not really a solid argument at all. They just have to work around the mistakes they made in the past (no value types + runtime type erasure). We also know for a fact that escape analysis in JVM doesn't really cover that many cases anyway in practice. You need to look at the generated code to tell if it works or not. Besides, it is not something that the CLR cannot implement. On the contrary, there is active effort in CLR towards Object Stack Allocation (you can Google for it).

The general point that reflection is "only" needed because of a "weak static type system" is also not true. You seem to confuse the shape of the API for getting runtime type information with the need for getting such information in the first place. You can try to build a polymorphic serializer in C++ which also has run time type erasure, it is not as easy as in C#. Eventually we need to carry over type information anyway, no matter what language.

Reflection is not about "adding info about type parameters at runtime". It is much more than that. First, we don't "add information" at runtime for existing types, we can inquire about it. This is super useful for many scenarios. Second, we can generate code at runtime as well with reflection, that is, MSIL op codes. This is also super useful.

Your use case of "express sum function over Array<A>" is not the direction C# is heading. We have LINQ for the expressiveness part which Java doesn't have apart from some lookalike hacks. Also, for performance, your sum function is going to run at glacier speed compared with .NET Core 3.0 where we will have SIMD instructions and we can execute dedicated AVX code paths depending on memory alignment, in managed code. This stuff used to be C++ only until now. I don't think your Scala and Haskell implementations stand a chance to perform close to that. And reusing a sum function over a read only span is a matter of a one line call. I like the pureness argument but in practice we need to consider performance as well.