Two possibilities of fixing format problem, which is better?

[berni44]

On Monday, 21 October 2019 at 07:18:09 UTC, berni44 wrote:
> On Sunday, 20 October 2019 at 23:15:28 UTC, rikki cattermole 
> wrote:
>> What does printf do?
>
> b) :-) Thanks.

Unfortunately, meanwhile I learned, that there are various 
implementations of printf with different behaviour. So it doesn't 
really answer my original question.

Here an example:

import std.stdio;

int[] a = [1,23,-456];
writeln(format("%20s",a));
writeln(format("[%(%20s%|, %)]",a));

produces:

[                   1,                   23,                 -456]
[                   1,                   23,                 -456]

but IMHO the first line should be:

        [1, 23, -456]

This is in accordance with the current Phobos spec and some 
printf spec I found in the internet. Should this be corrected?

Similar:

import std.stdio;

char[] a = ['a','b','c'];
writeln(format("%20s",a));
writeln(format("[%(%20s%|, %)]",a));

produces:

                  abc
['a', 'b', 'c']

And:

import std.stdio;

String[] a = ["a","b","c"];
writeln(format("%20s",a));
writeln(format("[%(%20s%|, %)]",a));

produces:

["a", "b", "c"]
["a", "b", "c"]

So my question remains: What is considered correct behaviour here?