The Benefits of Constants

Question

I understand one of the big deals about constants is that you don\'t have to go through and update code where that constant is used all over the place. Thats great, but let\'s s

Answer 1

It's possible that the compiler could reduce code size .. for example, in package System you'll find (on an x86 machine)

type Bit_Order is (High_Order_First, Low_Order_First);
Default_Bit_Order : constant Bit_Order := Low_Order_First;

so that given

case System.Default_Bit_Order is
   when System.High_Order_First =>
      --  Big-endian processing
   when System.Low_Order_First =>
      --  Little-endian processing
end case;

the compiler can completely eliminate the 'wrong' branch while your code retains its portability. With GNAT you need to use non-default optimisation for this to happen: -O2 I think.

Both branches have to be compilable -- this is an optimisation, not #ifdef processing.