Hi
Would you please teach me what's wrong with the following code?
I would like to pass a D function to a C function as a callback.
I could not figure it out what is wrong from the error message.
#### Error
````console
$ dub
...
Building test ~master: building configuration [application]
src/main.d(8,6): Error: function `run` is not callable using
argument types `(extern (C) int function())`
run(&callback);
^
src/main.d(8,6): cannot pass argument `& callback` of type
`extern (C) int function()` to parameter `extern (C) int
function() fn`
src/test.c(3,5): `test.run(extern (C) int function() fn)`
declared here
int run(fp fn) {
^
````
#### Code
````d
// src/main.d
import test;
extern (C) int callback() {
return 0;
}
auto main() {
run(&callback);
}
````
````c
// src/test.h
typedef int(*fp)();
int run(fp);
````
````c
// src/test.c
typedef int(*fp)();
int run(fp fn) {
return fn();
}
````
````
// dub.sdl
name "test"
targetType "executable"
mainSourceFile "src/main.d"
sourceFiles "src/test.c"
cImportPaths "src"
````
#### Compiler
````console
$ ldc2 -v
binary .../ldc/ldc2-1.42.0-osx-arm64/bin/ldc2
version 1.42.0 (DMD v2.112.1, LLVM 21.1.8)
config .../ldc/ldc2-1.42.0-osx-arm64/etc/ldc2.conf
(arm64-apple-darwin25.5.0)
````
#### It works when not using `ImportC`
````d
// src/main.d
extern (C) int run(int function());
extern (C) int callback() {
return 0;
}
auto main() {
run(&callback);
}
````
But I would like to know how to compile the code with `ImportC`.
