On 7/4/23 11:15 AM, kiriakov wrote:
On Tuesday, 4 July 2023 at 14:42:31 UTC, Steven Schveighoffer wrote:
On 7/4/23 10:19 AM, kiriakov wrote:
On Tuesday, 4 July 2023 at 12:43:19 UTC, Steven Schveighoffer wrote:
On 7/4/23 12:58 AM, kiriakov wrote:
It looks like a type mismatch. The function accepted should return
`Result` but it's returning `ParsResult`.
That's the problem
Result(T) = SumType!(ParsResult!T, Err!T)
No, `Result(T)` is its own struct in your example.
And also, `SumType!(ParsResult!T, Err!T)` is not the same as
`ParsResult!T`. function pointers must match the return type.
I was recommended:
https://forum.dlang.org/thread/iblsgqqafagdgcsaf...@forum.dlang.org
```
struct Result(T) {
SumType!(ParsResult!T, Err!T) data;
alias data this;
this(Value)(Value value) { data = value; }
}
```
You misunderstand, the function return type must match. If you want to
accept a function pointer that returns Result, you must specify the
function type as returning Result. It can't return something else, and
still be the same type of function pointer.
D unfortunately does not obey covariance or contravariance with function
pointer return types, but even if it did, in this case it would not work.
-Steve
