If a company in which you held shares was taken over and you received new shares in the takeover company, you may be entitled to scrip-for-scrip roll-over for any capital gain you made. Usually, the takeover company would advise you if the scrip-for-scrip roll-over conditions were satisfied.
If you also received some cash from the takeover company you would only be entitled to a partial roll-over.
If the scrip-for-scrip conditions were not satisfied, your capital proceeds for your original shares will be the total of any cash and the market value of the new shares you received.
Scrip-for-scrip roll-over may also be available to the extent that units in a managed fund are exchanged for units in another managed fund.