Immutable woes

[Bob Cowdery]

 Hi

I'm stuggling with immutable.

I have a fixed size buffer which is used as a circular buffer of floats
and is effectively double buffering data I wish to transfer to another
thread. At an appropriate point I take the top half or bottom half of
the buffer and send it to another thread.

To do this I need to copy the data to an immutable transfer buffer to
use in the send. I'm sure this is simple but I can't figure it.

if I say something like:
float[] xfer = new float[512];
xfer = buffer[0 .. $/2];
tid.send(xfer);

it rightly tells me 'thread local data not allowed'. If I make it:

immutable (float)[] xfer;
xfer = buffer[0 .. $/2];
tid.send(xfer);

it tells me 'can't implicitly convert float[] to immutable (float)[]'

If I try a float by float copy into xfer it can't because I've said the
buffer is immutable. In the first example I can't figure out how to
convert the slice into an immutable copy which I think is what I should
be doing.

Can someone point me in the right direction.

Thanks
Bob