The BFlattenable class declares a protocol for objects that can be flattened—written to an untyped buffer of bytes—and unflattened from the buffer. By implementing this protocol, a class gives others the ability to manipulate its objects in a flexible manner. Currently, only the BMessage class, through its AddFlat() and FindFlat() functions, declares an API that can deal with BFlattenable objects. The BPath class in the Storage Kit derives from BFlattenable.

As this class merely declares a protocol for other classes to implement, it doesn't include a constructor or destructor.