Manifest Constants

Manifest constants are variables evaluated at compile time. They cannot change their value. A manifest constant is declared by using the keywork enum:

enum i = 4;      // i is 4 of type int
enum long l = 3; // l is 3 of type long

Manifest constants are not lvalues, meaning their address cannot be taken. They exist only in the memory of the compiler. Declaring a manifest constant that cannot be evaluated at compile time is an error:

void main()
{
    int a = 5;
    enum b = 5 + 2;   // ok, '5' and '2' are integer literals, known at compile time
    enum b = a + 2;   // error: 'a' cannot be read at compile time  
}

To make the above code work, a should be declared as an enum.

Manifest constants can be seen as compile time variable declarations.

Practice

Go to this link. You will find the disassembly of a code. Observe how the call to function sum is translated in assembly code. Explain the output.