Discussion on static reflection syntax in C++

[Bruce Carneal]

On Monday, 22 February 2021 at 23:44:45 UTC, Paul Backus wrote:
>
> As far as I'm concerned, a procedural macro is a function that
>
> 1. runs at compile time,
> 2. takes AST nodes as input, and
> 3. produces AST nodes as output.
>
> Type functions fit those criteria perfectly. Currently, they 
> only work on a subset of AST nodes (types), so they're not a 
> *complete* implementation of procedural macros, but generalize 
> them enough and that's what you'll get.

Yes.

Given the collective experience that we've had with D's meta 
programming facilities it would be surprising if we could not 
imagine something significantly better at this point.  By 
"better" I mostly mean facilities that would allow us to write 
code that is more readable, more composable, more testable, and 
more easily debuggable than an equally performant solution using 
current practice.

I'm sympathetic to both type functions and MTVs (monadic type 
variables), CT type objects with actual memory footprint that 
function as compiler-guaranteed-safe cursors within the lazily 
realized dependent type space of a D program.

Beyond those two I know that Stefan, and from the above and 
earlier writings I expect Paul, have thought about more powerful 
yet still tractable capabilities.  It feels like we're within 
reach of a significant advance.