Template argument deduction fails with alias

[Ben Jones]

On Tuesday, 1 September 2020 at 01:26:30 UTC, Paul Backus wrote:

>
> Aside from using SumType directly in the function signature, 
> another workaround is to use a wrapper struct instead of an 
> alias:
>
>     struct AliasType(Args...) {
>         SumType!Args data;
>         alias data this;
>     }
>
>     bool func(T : AliasType!Args, Args...)(T t) { ... }

Thanks all.

I tried using alias this at first and then I get errors trying to 
construct AliasType objects:


auto pi = Payload!int(5);
auto pe = ParseError("error");
alias PRType = ParseResult!(Payload!int, ParseError);
auto pr = PRType(pi);

gives:

cannot implicitly convert expression `pi` of type `Payload!int` 
to `SumType!(Payload!int, ParseError)`