static const Member Value vs. Member enum : Which Method is Better & Why?

Question

If you want to associate some constant value with a class, here are two ways to accomplish the same goal:

class Foo { public:     static const size_t Life = 42; };  class Bar { public:     enum {Life = 42}; }; 

Syntactically and semantically they appear to be identical from the client's point of view:

size_t fooLife = Foo::Life; size_t barLife = Bar::Life; 

Is there any reason other than just pure style concerns why one would be preferable to another?

Answer 1

The enum hack used to be necessary because many compilers didn't support in-place initialization of the value. Since this is no longer an issue, go for the other option. Modern compilers are also capable of optimizing this constant so that no storage space is required for it.

The only reason for not using the static const variant is if you want to forbid taking the address of the value: you can't take an address of an enum value while you can take the address of a constant (and this would prompt the compiler to reserve space for the value after all, but only if its address is really taken).

Additionally, the taking of the address will yield a link-time error unless the constant is explicitly defined as well. Notice that it can still be initialized at the site of declaration:

struct foo {     static int const bar = 42; // Declaration, initialization. };  int const foo::bar; // Definition.