Wanted: Format character for source code literal

[Berni44]

On Tuesday, 4 May 2021 at 18:02:50 UTC, Q. Schroll wrote:
> So you're stuck between a rock and a hard place: Give `%D` 
> preference over custom format specifiers rendering those that 
> use `%D` invalid or let `%D` do its custom stuff if 
> *potentially* supported rendering `%D` useless in generic code 
> where most of its use-cases would lie.

I fear, I can't follow you. Seems like I don't get your point. 
Maybe you can give an example?

>> In my opinion, the main idea behind this formatting routines 
>> is, to have a simple and short way for formatting output. We 
>> could use your idea for every other format character too, 
>> like: `format("%s = %s", character('𝜋'), 
>> scientificFloatingPoint(3.14))`. We don't do that, because 
>> it's more convenient to write `format("%c = %e", '𝜋', 3.14)`.
>
> Yes, you could. But you could use format specifiers like 
> `%-3.8f` *without losses* to get to the same result.

??? Again I'm stuck. What has `%-3.8f` with what I wrote above to 
do?

> And that's *the* difference between introducing a format 
> specifier character that should have generic meaning and 
> introducing, well, anything else. There was no problem 
> introducing separators like `%,3d` and neither would there be a 
> problem introducing `%y` for `int` or `double` (whatever it 
> does), or, for a concrete example, `%S` for `bool` to return 
> `TRUE` instead of `true`.
>
> The problem is introducing *generic* format specifier 
> *characters*.

What is the difference between "generic" (which as far as I 
understand you oppose) and adding `%D` for bool, integers, 
floats, characters, strings, arrays and AAs (which you sound as 
being OK with, and which is, what I plan to do)?

> What we could do is special casing `%$` to mean what you want. 
> Currently, no matter what type you're formatting, `%$` is an 
> error in `FormatSpec`. You can give it semantics, no problem, 
> including one that ignores custom formatting. Even better, `%$` 
> looks like it's a special case and not some odd-but-legal 
> custom specifier.

Using `$` would cause real troubles, because it's already used 
for positional arguments. What would `format("%1$d", 'a');` be 
supposed to produce? `'a'd` or `97`?

> Changing the meaning of `%D` begs for trouble.

`%D` has currently no meaning, so we cannot change it; we can 
just add it.


I hope, we can figure this out somehow - I sense, that you've got 
an important point, but I don't understand it. Seems like we are 
talking past each other.