public delegate weak Buffer BufferListDoFunction
A function for accessing the last buffer returned by next.
The function can leave
buffer in the list, replace
buffer in the list or remove
buffer from the list,
depending on the return value. If the function returns NULL,
buffer will be removed from the list, otherwise
will be replaced with the returned buffer.
The last buffer returned by next will be replaced with the buffer
returned from the function. The function takes ownership of
buffer and if a different value than
buffer is returned,
buffer must be unreffed. If NULL is returned, the buffer will be removed from the list. The list must be writable.
|the buffer to replace
buffer in the list, or NULL to remove
buffer from the list