Reimplementing the bulk of std.meta iteratively

[Steven Schveighoffer]

On 9/29/20 8:02 AM, Patrick Schluter wrote:
> Your AA example is a good one. If it wasn't in the language, it would be 
> the same issue with AA as in any other language that defines it in 
> libraries: several different incompatible restricted implementations.

AA is not that far from being a library type.

If you discount the magic casting that AAs can do (which isn't all that 
useful), there is one (yes ONE) feature that AAs do that a library type 
cannot. And that is an implicit adding of an element in certain cases. 
The reason AAs can do it is because the compiler calls a different 
opIndex (it's not called opIndex, but some extern(C) hook) when it's in 
this mode, but only for AAs.

In fact, AAs are mostly already a library type, thanks to a lot of 
incremental effort over the years to lower the implementation to 
templates. Except for this one thing.

-Steve