On Saturday, 20 September 2025 at 03:01:55 UTC, Paul Backus wrote:
On Saturday, 20 September 2025 at 01:46:47 UTC, monkyyy wrote:
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
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.
thoughts on this direction?
```d
#!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
}
```
