Is std.variant useful for types only known at run time?

[Steven Schveighoffer]

On 9/8/21 5:55 AM, Chris Piker wrote:
> On Wednesday, 8 September 2021 at 08:39:53 UTC, jfondren wrote:
>> so I'd look at a std.sumtype of them first:
> 
> Wow, this forum is like a CS department with infinite office hours!
> 
> Interesting.  I presume that the big win for using std.sumtype over a 
> class set is value semantics instead of reference semantics?
> 
> So out of curiosity, say each structure implemented a function to 
> provide the desired broken-down-time, would the following "virtual 
> function" style call work?
> 
> ```d
> import std.sumtype;
> struct BDTime { int y, int m, int d, int h, int m, double s };
> 
> struct ISO8601 { BDTime bdTime(){ ... }  }
> struct FloatEpoch { BDTime bdTime(){ ... } }
> struct DoubleEpoch { BDTime bdTime(){ ... } }
> struct LongEpoch { BDTime bdTime(){ ... }  }
> alias Time = SumType!(ISO8601, FloatEpoch, DoubleEpoch, LongEpoch);
> 
> void main() {
>      import std.stdio : writeln;
>      import std.format : format;
> 
>      Time e = ISO8601();
>      BDTime = e.bdTime();
> }
> ```
> or would I need to use `match!` to get the right structure type and then 
> generate the internal time representation?
> 
> 

Just as an aside, 
[taggedalgebraic](https://code.dlang.org/packages/taggedalgebraic) does 
this for you.

-Steve