On Monday, 21 February 2022 at 20:18:46 UTC, Paul Backus wrote:
This is a long-standing limitation of the D compiler's template
argument deduction: it cannot "see through" `alias` templates
to deduce the underlying type.
Oh, that’s an unfortunate limitation but at least there’s a
workaround.
On Monday, 21 February 2022 at 18:43:18 UTC, Emmanuelle wrote:
If you run this, the compiler should emit this error:
```d
onlineapp.d(14): Error: template `onlineapp.foobar` cannot
deduce function from argument types `!()(SumType!(int, Unit))`
onlineapp.d(8):Candidate is: `foobar(T)(Opt
See https://run.dlang.io/is/hNaSFh:
```d
import std.sumtype;
struct Unit {}
alias Option(T) = SumType!(T, Unit);
void foobar(T)(Option!T option) {}
void main() {
foobar(Option!int(123));
}
```
If you run this, the compiler should emit this error:
```d
onlineapp.d(14): Error: template `on
