Reimplementing the bulk of std.meta iteratively

[Sebastiaan Koppe]

On Thursday, 8 October 2020 at 10:16:10 UTC, Stefan Koch wrote:
> This is the correct type function way of doing it:
> enum type[] types = makeTypeArray(int, uint, long, ulong);
> enum type[] size4 = types.filter!((type a) => a.sizeof == 4);
> static assert(equal!((type a, type b) => a is b) (size4, 
> makeTypeArray(int, uint)));
>
> Currently type[] fails is isInputRange though and therefore the 
> phobos filter won't instantiate.
> I am debugging this.

This is plain awesome.

The fact that it reuses the filter algorithm is a sign that both 
filter and type functions are correctly designed.

Who could ever imagined that a template would be instantiated 
with a lambda that takes a type-value as an argument. WAT!? That 
is some high-order stuff, and perfectly readable.

Andrei's de/reify is awesome as well, it has the advantage of 
working with existing language constructs, but it isn't as simple.