On Saturday, 15 February 2025 at 19:49:59 UTC, monkyyy wrote:
code
```d
import std;
struct nullable(T){
T get_; alias get_ this;
bool isnull=false;
int classify()=>isnull;
enum classmax=2;
alias get(int i=0)=get_;
}
unittest{
nullable!int foo;
}
template match(F...){
auto match(T)(T t){
switch(t.classify){
static foreach(I;0..T.classmax){
case I: return F[I](t.get!I);
}
default: assert(0);
}}}
unittest{
nullable!int foo;
void bar(nullable!int
i)=>i.match!((a){"real".writeln;},(a){"null".writeln;});
bar(foo);
int foobar(nullable!int i)=>i.match!(a=>1,a=>2);
foobar(foo).writeln;
foo.isnull=true;
bar(foo);
foobar(foo).writeln;
}
struct smallint{
int i;
int classify()=>i<=ubyte.max && i>=0;
enum classmax=2;
ubyte get(int i:1)()=>cast(ubyte)i;
alias get(int i:0)=i;
}
unittest{
foreach(i;[0,4,10,1000,1].map!(i=>smallint(i))){
i.match!(a=>"error",a=>"fine").writeln;
}}
union U{
ubyte i;
char c;
float f;
}
struct tagunion{
int classify;
U u; alias u this;
enum classmax=3;
auto get(int i:0)()=>u.i;
auto get(int i:1)()=>u.c;
auto get(int i:2)()=>u.f;
}
unittest{
tagunion foo;
void bar(tagunion u){u.match!(writeln,writeln,writeln);}
foo.i=3;
bar(foo);
foo.classify=1;
foo.c='z';
bar(foo);
foo.classify=2;
foo.f=13.37;
bar(foo);
}
```
