@dotnet/ilc-contrib Should Array.Initialize be marked with RequiresUnreferenceCode, or is the value type default constructor the special-cased by the trimmer and always preserved?

I think it should:

var b = new ElementType[1];
b.Initialize();

struct ElementType
{
    public ElementType()
    {
        Console.WriteLine(".ctor called");
    }
}

dotnet run prints out ".ctor called".
But trimmed the app doesn't print out anything.

Related question - what should default do in this case, for example:

var c = new ElementType[1];
c[0] = default; // Should this call the default .ctor?

Running it seems like it will NOT call the .ctor - but what does it do?

Same goes for AOT - published as Native AOT the app above also doesn't print out anything.

Related question - what should default do in this case, for example:

According to the specification, default ignores the parameterless constructor and generates a zeroed instance.

Hmmm, adding RequiresUnreferencedCode on Array.Initialize has a ripple effect. It introduces warnings in situations where array type is passed into DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All).

I guess it will need more careful thought.

Opened #77426

@reflectronic Are you up for implementing the mono version mostly in C#, too?

I think we can add something like NativeAOT's default constructor -> function pointer icall and then most of this code could be managed.

We don't need to do it in this PR (unless you want to). Just an idea.

I would have done it like that, but I couldn't quite find the function I wanted (wasn't sure if the thing I was looking at was safe to just call with calli, whether it would try to unbox the argument, etc.). Certainly, I could address it in a follow up.

@reflectronic I don't think there's an existing icall, but it should be ok to add something like this:

MonoMethod * const method = mono_class_get_method_from_name_checked (element_class, ".ctor", 0, 0, error);
if (!method) {
	return NULL;
}
gpointer addr = mono_compile_method_checked (method, error);
if (!is_ok (error)) {
	mono_error_cleanup (error);
	return NULL;
}
return mono_create_ftnptr(addr);

on the C# side it would look pretty much like the NativeAOT version - cast the icall's IntPtr result to a function pointer type and call it.

wasn't sure if the thing I was looking at was safe to just call with calli, whether it would try to unbox the argument, etc.

I'm pretty certain that it will just work. I believe it should be expecting an unboxed argument.