On Monday, 13 June 2022 at 20:25:00 UTC, Steven Schveighoffer
wrote:
On 6/13/22 4:09 PM, JG wrote:
Thanks. It seems to be something to do with the variadic
template since this
works:
```d
import std;
struct ParseError { string msg; }
alias ParseErrorOr(T) = SumType!(ParseError,T);
auto parseErrorOr(T)(T x) { return ParseErrorOr!T(x); }
auto parserOr(I,alias f, alias g)(I i) {
auto cur = f(i);
if(cur.match!((ParseError e)=>false,_=>true)) { return cur;
}
return g(i);
}
auto parseNothing(I)(I i) {
return parseErrorOr(tuple(i[0..0],i));
}
void main()
{
enum a =
parserOr!(string,parseNothing!string,parseNothing!string)("hello");
}
```
Given that it's inside `moveEmplace`, I'd suspect something
deep in `SumType`.
-Steve
Really strange. I can also work around it like this:
```d
auto parserOr(I,fs...)(I i) if(fs.length>=2) {
auto cur = fs[0](i);
if(cur.match!((ParseError e)=>false,_=>true)) { return cur;
}
static if(fs.length==2) { return fs[1](i); }
else { return parserOr!(I,fs[1..$])(i); }
}
```
