The flags field in the marshalling type annotation must be an array of identifiers, providing anything else will result in this error.
The following examples generate CPP0008.
@:semantics(value) @:cpp.ValueType({ flags : StackOnly }) extern class Foo { function new():Void; } function main() { final f = new Foo(); }
@:semantics(value) @:cpp.ValueType({ flags : [ 'StackOnly' ] }) extern class Foo { function new():Void; } function main() { final f = new Foo(); }