Using output-range overloads of SysTime.toISO{Ext}String with formatting code

[Digital Mars]

08.07.2019 13:38, Joseph Rushton Wakeling пишет:
> 
> Thanks for taking the time to answer, but I don't think this really 
> addresses my question.
> 
> Your example shows a struct with `toString` overloads.  However, 
> SysTime.toISOExtString does not work like this: it is a method with two 
> explicit overloads, one of which just returns a newly allocated 
> `string`, the other of which returns nothing but accepts an output range 
> as input:
> https://dlang.org/phobos/std_datetime_systime.html#.SysTime.toISOExtString
> 
> I want to know if there's an easy way to work with that in `format` and 
> `writefln` statements.
> 
> Note that while SysTime does also have `toString` methods, these give no 
> control over the kind of datetime string that results:
> https://dlang.org/phobos/std_datetime_systime.html#.SysTime.toString
> 
> Since I explicitly need the extended ISO format, I need to use 
> `toISOExtString` directly.
Sorry that my answer wasn't thoughtful.

I guess that there is no way to have `writeln` automatically use the 
output range overload instead of allocating one. You need somehow to 
provide the output range to `toISOExtString` explicitly because 
`writeln` outputs the return of `toISOExtString` and have no ability to 
use specific overload. That is compiler calls `toISOExtString` and then 
passes its return to `writeln`. Probably library solution isn't possible 
in this case. Workaround is using own wrapper to provide output range to 
`toISOExtString`.