I’m bridging a C API (that I wrote) to Swift; I’ve got most of it together, but I’m stuck on one part, where I can’t get the bridging code to compile without errors no matter how I write it.
The basic problem is I’ve got a dynamically-allocated opaque C pointer type (C4Key*), and there’s a struct in the C API with a field that points to a C array of these, plus a count. In Swift I have an array of these pointers, typed as [COpaquePointer], and I want to point the struct field to it.
Here’s the relevant bit of the C API:
typedef struct c4Key C4Key; // opaque type
C4Key* c4key_new(void);
typedef struct {
// ...
const C4Key **keys;
size_t keysCount;
} C4QueryOptions;
In my Swift code I have:
var opt = C4QueryOptions()
var keyHandles: [COpaquePointer] = wrappedKeys.map {$0.handle}
// Attempt 1, error is “Cannot assign [COpaquePointer] to COpaquePointer”:
opt.keys = &keyHandles
// Attempt 2, error is "cannot assign value of type 'UnsafePointer<[COpaquePointer]>' (aka 'UnsafePointer<Array<COpaquePointer>>') to type 'UnsafeMutablePointer<COpaquePointer>'"
withUnsafePointer(&keyHandles) { keysPtr in
opt.keys = keysPtr
DoSomethingWith(opt)
}
It’s definitely a type-checking problem; I can’t convince the compiler to give me a pointer to the elements of the array as a COpaquePointer. Any clues?
—Jens