Idea: extern static fields

[jkrejcha]

C# has the ability to reference externally defined functions like so

public static extern ReturnType ExternFn();

but isn't able to reference externally defined fields in the same way that C code might. This is useful for some interop scenarios where a exported field is defined.

Syntax proposal would probably be similar to

public static extern FieldType ExternField;

Currently the only alternative is to use the NativeLibrary.GetExport function.

[huoyaoyuan]

How does C++/CLI handle this? Does the runtime and ECMA-335 have feature to support this?

[colejohnson66]

C and C++ (non CLI) do have the ability to access static "fields" defined in external libraries. It's how errno works. I'd assume C++/CLI then would support it.

[huoyaoyuan]

I'd assume C++/CLI then would support it.

Nope, C++/CLI doesn't support all features natively. If it uses native code as a bridge, it will not be a solution for managed code.

[jkrejcha]

extern fields do work in C++/CLI as far as I can tell but generate a link-time error if it can't resolve the external then. It doesn't use P/Invoke there from what I can tell though and just relies on the external being available at link time.

As far as ECMA-335, it looks like it does as pinvokeimpl is supported for fields (see p. 251 (277 in PDF)) as well as methods so it doesn't look like any CIL change would be required.

Not 100% sure on the runtime front but from a cursory glance it mostly assumes that P/Invoke applies to methods only.

[Unknown6656]

[huoyaoyuan]

Exporting are quite different from importing.

[Unknown6656]

I'm terribly sorry. I must have somehow misread the proposal yesterday (don't ask me how or why). I deleted my comment.