• NonNull (15/15) Sep 20 2021 How do I write the type of a function so as to alias it, and use
• Paul Backus (14/20) Sep 20 2021 You can create an alias to the type:
• Tejas (3/18) Sep 20 2021 This is for C++, but I think you'll find it helpful all the same

NonNull <non-null use.startmail.com> writes:

How do I write the type of a function so as to alias it, and use 
that in an extern(C) declaration?

For example, how do I write the type of an external function

int main2(int argc, char** argv) {
     //
}

?

This is not

int function(int, char**)

because this is the type of a function pointer of the right type, 
not the type of the function itself.

If I had that type aliased to mainfunc I could write

extern(C) mainfunc main2;

in D source to arrange to call it, and similarly any other 
functions of the same type.

Paul Backus <snarwin gmail.com> writes:

On Monday, 20 September 2021 at 20:02:24 UTC, NonNull wrote:
 How do I write the type of a function so as to alias it, and 
 use that in an extern(C) declaration?

 For example, how do I write the type of an external function

 int main2(int argc, char** argv) {
     //
 }

You can create an alias to the type:

```d
alias MainFunc = int(int, char**);
```

However, you can't use that alias to declare a variable, because 
variables are not allowed to have function types:

```d
MainFunc main;
// Error: variable `main` cannot be declared to be a function
```

The only way you can declare a function in D is with a [function 
declaration.][1]

[1]: https://dlang.org/spec/function.html#FuncDeclaration

Tejas <notrealemail gmail.com> writes:

On Monday, 20 September 2021 at 20:02:24 UTC, NonNull wrote:
 How do I write the type of a function so as to alias it, and 
 use that in an extern(C) declaration?

 For example, how do I write the type of an external function

 int main2(int argc, char** argv) {
     //
 }

 ?

 This is not

 int function(int, char**)

 because this is the type of a function pointer of the right 
 type, not the type of the function itself.

 If I had that type aliased to mainfunc I could write

 extern(C) mainfunc main2;

 in D source to arrange to call it, and similarly any other 
 functions of the same type.

This is for C++, but I think you'll find it helpful all the same

https://atilaoncode.blog/2019/03/07/the-joys-of-translating-cs-stdfunction-to-d/