Challenge: write a template-instance free dispatcher for text printing

[Paul Backus]

On Wednesday, 27 May 2026 at 18:13:40 UTC, H. S. Teoh wrote:
> Although D templates are extremely powerful and awesome for 
> metaprogramming, templates are ultimately not the right concept 
> for many CT tasks. What we *really* want is CTFE + type 
> manipulation for DbI to compute the final form of a template 
> instantiation, then a single template instantiation at the end 
> to actualize it.  The current idiom of arbitrarily-complex 
> templates nested arbitrarily deep, while powerful, leads to 
> needless template bloat.

What you're describing is Lisp macros, and Walter has gone on 
record many, many times that D will never have them.

I think the best we can do is probably something similar to C++'s 
{fmt} library, which uses type erasure and runtime dispatch to 
avoid unnecessary template instantiations. For example, if we are 
formatting 5 different structs that all have toString() methods, 
there is no need to instantiate 5 completely separate copies of 
writeln--instead, we can have one instance of writeln which makes 
an indirect call through an interface/delegate, and 5 instances 
of a small helper function which that interface/delegate can 
dispatch to.