newbie question about decoder

[Max]

is it correct to implement a decoder in the following way?

reg_en <= "000" when ce = '0' else
"001" when cpu_addr_bus = "00" else
"010" when cpu_addr_bus = "01" else
"100" when cpu_addr_bus = "10" else
"000";

ce is the decoder enable. Once ce is one I decode cpu_addr_bus.

thanks