Message CS0193 is misleading in the context of a function pointer

[RexJaeschke]

Type of issue

Missing information

Description

I'm working on the ECMA C# spec for V9's function pointers.

Consider the following code fragment:

public static void Log() { ... }

delegate*<void> fp = &Log;   // pointer to managed function Log()
fp();                       // OK; call Log() via function pointer
(*fp)();                   // Error; CS0193, "The * or -> operator must be applied to a pointer"

When fp is a function pointer in C/C++, both of the final 2 statements are allowed and are equivalent, so I tried both in C#.

However, in C#, a function pointer cannot be dereferenced, and that is why the second call is rejected.

Perhaps the simplest fix is to change (preferably in the compiler, but at least in the docs)

CS0193: The * or -> operator must be applied to a pointer

to

CS0193: The * or -> operator must be applied to a data pointer

which then excludes function pointers and void pointers.

And then add

A function pointer cannot be dereferenced.

BTW, I note that attempting to dereference a void pointer results in CS0242, "The operation in question is undefined on void pointers", so that need not be mentioned here.

Page URL

https://learn.microsoft.com/en-us/dotnet/csharp/misc/cs0193?f1url=%3FappId%3Droslyn%26k%3Dk(CS0193)

Content source URL

https://github.com/dotnet/docs/blob/main/docs/csharp/misc/cs0193.md

Document Version Independent Id

43bae4fc-fe3e-033d-8f16-e8bffaebf202

Platform Id

adbc4b45-657e-029c-fd2e-d875421f318b

Article author

@BillWagner

Metadata

• ID: 6f680362-c4bd-95d6-2cad-99e77e847cd0
• PlatformId: adbc4b45-657e-029c-fd2e-d875421f318b
• Service: dotnet-csharp
• Sub-service: errors-warnings

Related Issues

---

Associated WorkItem - 436203