Manifest constants: why enum instead of invariant?

[Bill Baxter]

Bruno Medeiros wrote:
> Picking up and idea which had crossed my mind, and that Oskar Linde 
> briefly mentioned on the const debacle thread 
> (news://news.digitalmars.com:119/fsirc9$2hll$1@digitalmars.com):
> 
> Why do we need enum instead of invariant to declare manifest constants?
> 
> (I have the feeling that this has been discussed before in the manifest 
> constants debate but I can't remember it nor find it)
> 
> An invariant variable offers all the power than enum does for manifest 
> constants. The only difference of enum's manifest constants is that they 
> are not an lvalue (their address cannot be taken). But that's a 
> *restriction*, it's not a useful property.
> 
> The only possible advantage I see is that of optimization: manifest 
> constants do not take up space. But that *hardly* seems significant: 
> manifest constants are usually numeric, and thus occupy about 2-4 bytes 
> each. Even if they are many, in total they are not going to occupy that 
> much space. A string literal can easily occupy as much space as several 
> manifest constants, and they are likely going to be many string literals 
> abound.
> 

The space *is* a significant problem apparently.  There have been many 
complaints about the size added to an exe simply by linking in early 
versions of the Windows headers because of all the constants they define.

But I suppose you could also look at that and say "we need to fix the 
linker & optimizer" instead of "we need to fix the language".

--bb