Compile-time variables

[Kayomn]

On Friday, 6 April 2018 at 00:21:54 UTC, H. S. Teoh wrote:
> On Thu, Apr 05, 2018 at 11:53:00PM +0000, Kayomn via 
> Digitalmars-d-learn wrote: [...]
>> [...]
> [...]
>> [...]
>
> `lastID`, as declared above, are runtime variables. The 
> 'static' in this case just means it's thread-local, rather than 
> allocated on the stack. You cannot modify these variables at 
> compile-time.
>
>
>> [...]
>
> You appear to be wanting to increment a global variable during 
> compile-time. Unfortunately, there is no such thing as a 
> compile-time global variable.  You will have to find some other 
> way to implement what you want.
>
> One way to do this would be to use compile-time introspection 
> to construct a list of nodes, and then use a CTFE function or 
> static foreach to generate node IDs all at once.  For example:
>
> 	string generateEnum(T...)()
> 	{
> 		if (__ctfe) { // only run at compile-time
> 			string code = "enum NodeIds {";
> 			foreach (ident; T) {
> 				code ~= ident ~ ", ";
> 			}
> 			code ~= "}";
> 			return code;
> 		}
> 		else assert(0);
> 	}
>
> 	alias MyNodes = List!(
> 		// Just an example; you probably want to generate this
> 		// list via introspection, e.g. via __traits(getMembers)
> 		// or something like that.
> 		identifier1,
> 		identifier2,
> 		...
> 	);
>
> 	mixin(generateEnum!MyNodes); // defines `enum NodeIds`
>
> 	static assert(NodeIds.identifier1 == 0);
> 	static assert(NodeIds.identifier2 == 1);
> 	...
>
> There are probably other ways to do it too, but I chose enum 
> because it naturally assigns incrementing IDs to its members, 
> so it's a convenient construct for this purpose.
>
>
> T

I think I didn't explain well enough, I'm not trying to generate 
an enum from a list of pre-defined known quantities. The idea is 
that a compile-time generic function exists and it generates a 
unique identifier for that node.

My reasons for doing this is to remove the need to keep a master 
enum that holds an identifying value for each node. I've 
implemented this same thing in C++ before and it was extremely 
straightforward.