Load dynamic libraries with no hand-written bindings!

[Andrej Mitrovic]

On Wednesday, 7 September 2022 at 13:23:51 UTC, Paul Backus wrote:
> I'd say it's definitely a bug of some kind. This simplified 
> example worked for me:
>
> ```
> --- lib.c
> int f(int x) { return x + 1; }
>
> --- app.d
> import lib;
>
> typeof(&__traits(getMember, lib, "f")) fptr;
> pragma(msg, typeof(fptr)); // extern (C) int function(int x)
> ```

Reduced example:

```
--- lib.c
int foo( void );
typedef int Bar(const void *input);

--- main.d
import lib;

import std.meta;
import std.traits;

template FuncType(alias symbol) {
     alias FuncType = typeof(&symbol);
}

template GetFunctionList(alias Module) {
     alias GetFunctionList = AliasSeq!();
     static foreach (idx, member; __traits(allMembers, Module)) {
         static if (isFunction!(__traits(getMember, Module, 
member))) {
             GetFunctionList = AliasSeq!(GetFunctionList, 
typeof(&__traits(getMember, Module, member)));
         }
     }
}

alias X = GetFunctionList!lib;
void main() { }
```

Running:

```
$ dmd lib.c main.d

main.d(14): Error: `extern (C) int(const(void)* input)` is a 
`function` definition and cannot be modified
main.d(19): Error: template instance `main.GetFunctionList!(lib)` 
error instantiating
```

As mentioned in the previous reply it seems that a function 
typedef trips it up. If there was a way to filter it out, that'd 
be great.