On Tuesday, 3 June 2025 at 16:03:15 UTC, Andy Valencia wrote:
I have a Set data structure which has no concept of order; its
members are stored and can be searched efficiently based on
their hash.
I have a situation where chain()'ing them together would be
convenient, but InputRange requires front() and popFront().
There really _isn't_ a front, and creating a new Set with an
element removed would be unpleasant.
What would be the best way to iterate across a list of such
Set's? For now I'm just going to write the explicit loop.
Thanks!
Andy
```d
import std;
struct myset{
bool has3;
bool has5;
auto opBinary(string s:"+")(typeof(this) a){
return myset(has3||a.has3,has5||a.has5);
}
alias chain=opBinary!"+";
int front(){
if(has3){ return 3;}
if(has5){ return 5;}
assert(0);
}
void popFront(){
if(has3){has3=false; return;}
has5=false;
}
bool empty()=>( ! has3) && ( ! has5);
}
myset toset(R)(R r){
myset o;
foreach(i;r){
if(i==3){o.has3=true;}
if(i==5){o.has5=true;}
}
return o;
}
unittest{
myset a,b;
a.has3=true;
b.has5=true;
(a+b).writeln;
a.chain(a).chain(a).writeln;
b.chain(b).chain(b).writeln;
a.chain(b).writeln;
auto c=a+b;
c.map!(a=>a*2).writeln;
iota(10).filter!(a=>a==3).toset.chain(
iota(10).filter!(a=>a!=3).toset)
.writeln;
}
```
You can overload the names inside the datastructure and eagerly
lower it as needed
if you need it in something nested I have some more workarounds,
but they start to suck.
