On Tuesday, 24 February 2026 at 19:48:07 UTC, Julian Fondren
wrote:
On Tuesday, 24 February 2026 at 16:56:57 UTC, monkyyy wrote:
Its c-like code and enabling "unsafe" void* hacks.
Gist code from last night(I already see one improvement and
expect more):
```d
#!opend test app
import std;
import core.stdc.stdlib;
import core.sys.posix.dlfcn;
enum animalid{cow=7,chicken,horse};
struct animal{
animalid id;
string say;
int age;
}
...
```
An algebraic datatype, a sumtype, a discriminated union, etc.
And a 'fat pointer' is a just pointer to tagged data with some
Data-Oriented Design implications about the data. Wikipedia has
one good line about it:
Its an *intrusive* sumtype, fatpointers have different tradeoffs.
Also see me asking for help with intrusive lists.
A tagged union can be seen as the simplest kind of
self-describing data format. The tag of the tagged union can
be seen as the simplest kind of metadata.
With std.sumtype a 1:1 version of your code is a real pain, but
your method would be more painful if the variants weren't so
similar.
They are fat structs because you could have like 100 members.
There are ~3 details that I think can matter for overloading,
layout, different behavior, size.
Fat structs are making tradeoffs for layout similarity and I
expect dividends on the subject.
std.sumtype's also less painful over time, refusing
newanimal("idk"), having a compile-time exhaustiveness check.
There are some rough edges like .each! not working here.
Compile time exhaustiveness is a major tradeoff, even for
correctness focused code.
```d
struct foo{
string me;
bar* left;
bar* right;
}
alias bar=SumType!(null,int,float,bool,foo);
```
The recursion is hard to resolve; not impossible and I could
suggest 3 ideas, but still, this doesn't work with the 3 sumtypes
phoboes shipped.(1 of them was unjustifiably bad at this)
Skipping "do",
`Do` is the main point here, if you call `dlsym` your half way to
hotreloading. That sort of demo doesnt work well with a gist tho.
int age(Animal a) => a.match!(
(Cow a) => a.age,
(Chicken a) => a.age,
(Horse a) => a.age,
);
This is painful and would disqualify it if it was required, while
snar didnt get an `apply!(a=>a.age)` into phoboes it should be
entirely possible, I may have it somewhere, theres probably a
supported 2 line solution as well. My sumtype gists would be able
to implement it trivially.
unittest {
}
```
You also skipped "makechicken" and the effect that had on "say"
Its fun is a chicken says moo because it was raised a cow;
videogame logic, why not.
