Description
We could consider supporting unwrapping Strings to Pointers in FFI calls, this would make the following code much more ergonomic.
final messageBox = dl.lookupFunction<
Pointer Function(Pointer, Pointer<Utf16>, Pointer<Utf16>, Int32),
Pointer Function(Pointer, Pointer<Utf16>, Pointer<Utf16>, int)>();
final result = using((Arena arena) {
final message =
'This is not really an error, but we are pretending for the sake '
'of this test.\n\nResource error.\nDo you want to try again?'
.toNativeUtf16(allocator: arena);
final caption = 'Dart MessageBox Test'.toNativeUtf16(allocator: arena);
return messageBox(
NULL,
message,
caption,
MB_ICONWARNING | // Warning
MB_CANCELTRYCONTINUE | // Action button
MB_DEFBUTTON2 // Second button is the default
);
});New code, with the dart signature of messageBox having String rather than Pointer<Utf16> as argument types:
final messageBox = dl.lookupFunction<
Pointer Function(Pointer, Pointer<Utf16>, Pointer<Utf16>, Int32),
Pointer Function(Pointer, String, String, int)>();
final message =
'This is not really an error, but we are pretending for the sake '
'of this test.\n\nResource error.\nDo you want to try again?';
final caption = 'Dart MessageBox Test';
final result = messageBox(
NULL,
message,
caption,
MB_ICONWARNING | // Warning
MB_CANCELTRYCONTINUE | // Action button
MB_DEFBUTTON2 // Second button is the default
);We would have to specify the encoding expected, which we could do with the type argument of Pointer. The encoding would work exactly as package:ffi's toNativeUtf8() and toNativeUtf16() extension methods.
The life-time would be duration of the FFI call. (And for callbacks until the GC collects the String copied to Dart memory.)
For leaf-calls, if the string happens to be in the right encoding, we could pass the interior pointer. #39787 (comment)
One of the questions to answer is how to select the transform. Do we want support for more encodings than Utf8/Utf16? Do we always zero-terminate? And because the Utf16 and Utf8 are in package:ffi, do we move them?
Related: