Substitutions with writef() or format()?

[Ron Tarrant]

On Sunday, 14 July 2019 at 13:45:38 UTC, Ron Tarrant wrote:
> 'Morning, all.
>
> If these lines:
>
>    string currency = format("$%,.02f", 11_234_456.99);
>    writeln(currency);
>
> Will result in:
>
>    $11,234,456.99
>
> Why don't these lines:
>
>    string notCurrency = format("%,", 11_234_456);
>    writeln(notCurrency);
>
> result in:
>
>    11,234,456
>
> ???
>
> Instead of a range violation?

Never mind. This works:

    string notCurrency = format("%,?d", ',', 11_234_456);
    writeln(notCurrency);