Unification and extension of compile-time reflection

[Don]

Jarrett Billingsley wrote:
> Once upon a time, D did not have string mixins, or CTFE, or templates,
> or any of the fun things we have today.  Even so, it was still
> important to be able to access some information about types.  So
> Walter made it possible to query some basic information - the
> initialization value, minimum and maximum allowable values, byte size
> and alignment etc. - directly from the types as properties.  Neat.
> 
> Then D got templates.  D's templates were based on C++'s, to an
> extent, and therefore made use of specialization (and by corollary,
> SFINAE) to determine which template to instantiate.  By their nature,
> templates are a sort of way of introspecting types.  So now D has two
> ways to find out things about types.  Okay.
> 
> It turned out that templates were not always powerful enough - or
> sufficiently concise - to express some ideas.  So Walter came up with
> the is() expression (originally the "iftype" statement which begat
> "is()" and "static if") to query other, more interesting information
> about types.  It's _kind of_ like template specialization but has some
> extra features that specialization doesn't.  Now D has three ways to
> find out things about types.  Hm.
> 
> Along comes D2, and with it, the __traits keyword.  __traits is
> wonderful (except for the double-underscore name, anyway).  It's
> extensible, flexible, and can answer queries about types and other
> program objects in a way that would be extremely convoluted or cryptic
> if templates or the is() expression were extended.
> 
> But now D programs have _four_ ways to ask questions about themselves.

 > Some of these methods overlap but with wildly different syntax.

You left out typeof/typeinfo/typeid. There's run-time typeinfo, as well 
as compile-time. This is just begging for unification. Consider that in 
a CTFE function, you only use run-time syntax, but it's actually 
occuring at compile time.
And since Object now contains a factory method, there's considerable 
potential for deep unification.