std.format and uninitialized elements in CTFE

[berni44]

On Thursday, 5 December 2019 at 19:45:27 UTC, Steven 
Schveighoffer wrote:
> What is the point of formatting items that aren't initialized? 
> You would be printing garbage.
>
> What if you just initialize the items you wish to print,

You are on the wrong track... I'm programming inside of phobos. 
Such questions do not arise there. If the user provides a struct 
with (partially) uninitialized items std.format has to cope with 
this somehow. We cannot really answer the question, why the user 
is doing this, nor can we make him initialize the items before 
printing.

Ali's example shows, that this is a serious issue. IMHO my 
example should print `Foo(void)` or `Foo([void, void, void])` 
with `int[3]`. With that, Ali's example will work.

For me, the question remains, how to detect (at compile time) if 
a variable is void. The best I could come up with yet is:

int a = void;

static if (!__traits(compiles, a?a:a))

But I'm not sure if ?: can be applied to all thinkable types.