This was before my time. I was under the impression that it was somehow class and oo related badness when people talked about using TypeInfo; but when I my own experiments say that typeinfo is just another tool

I see 3k lines of code compared to my 50; Im going to say its but the postmorden seems wrong.

my code: https://gist.github.com/crazymonkyyy/14e36a99dd307c5d6e37bdb3ca2524a7

On Saturday, 20 September 2025 at 01:46:47 UTC, monkyyy wrote:

IMO there isn't really anything wrong with Variant. Given what it's trying to do, using TypeInfo or something similar is pretty much unavoidable. (Technically, Variant uses its own custom form of RTTI that's more lightweight than TypeInfo, but it still requires an extra level of indirection at runtime.)

The problem is with Algebraic, which uses RTTI even when all of the types are known at compile time--totally unnecessary.

On Saturday, 20 September 2025 at 03:01:55 UTC, Paul Backus wrote:

thoughts on this direction?

#!opend test app
import std;

struct introspectivepointer(alias F,T){
	void* me;
	T meta;
	void opAssign(T)(ref T t){
		me=cast(void*)&t;
		meta=F(t);
	}
	ref T get(T)(){
		assert(meta==F(*cast(T*)me));
		return *cast(T*)me;
	}
}

unittest{//sumtype-like
	introspectivepointer!(a=>typeid(a),TypeInfo) foo;
	foo=int(3);
	foo.get!int.writeln;//3
	foo=13.37;
	//foo.get!int.writeln;//error [unittest] double != int
}

unittest{//rip and tear
	struct vec2{int x,y;}
	struct circle{
		vec2 pos;
		int r;
	}
	struct rect{
		int w,h;
		vec2 pos;
	}
	introspectivepointer!(a=>a.pos.offsetof,ulong) shape;
	void move(typeof(shape) s){
		(*cast(vec2*)(s.me+s.meta)).y+=5;
	}
	auto foo=circle(vec2(1,1),5);
	auto bar=rect(3,5,vec2(3,3));
	shape=foo;
	move(shape);
	foo.writeln;//circle(vec2(1, 6), 5)
	shape.get!circle.writeln;//circle(vec2(1, 6), 5)
	shape=bar;
	move(shape);
	bar.writeln;//rect(3, 5, vec2(3, 8))
}
bool isNull(float f)=>f.isNaN;
unittest{//verify nullable
	Nullable!int i=15;
	introspectivepointer!(a=>tuple(typeid(a),a.isNull),Tuple!(TypeInfo,bool)) refi;
	refi=i;
	i=30;
	refi.get!(typeof(i)).writeln;//30
	i.nullify;
	//refi.get!(typeof(i)).writeln;//ugly but an error
	float f=13.37;
	refi=f;//!!!!!
	refi.get!float.writeln;//13.37
}