[uecker]

Every C compiler I ever used will tell you that void()(void) is not convertible to void ()(char). If people still do it then they are a bit on their own. But how is this then different to Rust's "unsafe"? (of course, there is other UB compiler do not tell you about, that this seems a bad example)

[im3w1l]

What if the function is written in assembler and takes some pointer to some opaque memory region?

void (*)(char *) and void (*)(void *) and even void\()(struct SomeStruct*) where SomeStruct is declared but never defined could all be correct and reasonable ways to declare that function in a c-header.