How to initialize immutable variables with an expression that throws an exception to catch?

[FeepingCreature]

On Friday, 3 April 2020 at 12:49:27 UTC, Steven Schveighoffer 
wrote:
> Do it the old-fashioned way -- use casting ;)
>
> S s_val = void;
> try
>   s_val = fun();
> catch (Exception)
>   return;
>
> immutable s = s_val.assumeUnique;
> call(s);
>

Doesn't work - `immutable struct` means S is always immutable.