Compile-time global mutables

[Paul Backus]

On Thursday, 30 June 2022 at 12:26:54 UTC, HuskyNator wrote:
> One example is generation of unique ID's (although there might 
> be some workarounds)

Here's a mixin that works for this particular use-case:

```d
enum gensym = q{"_gensym" ~ __traits(identifier, 
{})["__lambda".length .. $]};

// Works multiple times on the same line
pragma(msg, mixin(gensym)); pragma(msg, mixin(gensym));
```