C# Language Design Meeting for Jan 23, 2019

Agenda

Function pointers (Updated proposal)

Discussion

Creation of a function pointer to a managed method

The proposal is &Class.Method to produce a function pointer. The question is whether &Class.Method is target-typed, whether it has a natural type when there's only one member in the method group, or both.

Target-typing is useful because, like with delegates, it allows you to select a unique method out of a method group with multiple incompatible overloads.

Natural type is useful because it allows things like var and void*.

Conclusion

Let's start by only doing target-typing. Also, the section "better function member" is not necessary without the natural typing.

DllImport CallingConvention?

There is actually a stub that the compiler calls for P/Invoke with DllImport that is always done using the managed calling convention, so there's no reason for function pointers to use the DllImportAttribute.

NativeCallback is intended for the scenario where you want to avoid the stub overhead.

NativeCallableAttribute

Let's look at this in more detail.

Syntax

1. func* managed int(string)
2. func*(string)->int
3. func* managed (string)->int
4. func* managed (string)=>int
5. managed int(string)*
   5a. int(string)*
6. managed int(string)
7. managed (string)->int
8. delegate* int(string)
9. func int(string)*
10. delegate int(string)*

Conclusion

We're not sure about all the potential ambiguities here. Let's look at (5a), possibly disambiguating with the calling convention.

Things to clarify in spec

• What does the CLR do if you try to call a method that has a modreq/modopt in the signature, but the calli has the signature without the modreq/modopt?