std.format range with compound format specifiers?

[Steven Schveighoffer]

On 11/19/19 7:28 PM, Petar Kirov [ZombineDev] wrote:
> 
> In cases where I have some aggregate data, but I don't feel like writing 
> a custom toString method, I often wrap the data in a Tuple and use its 
> [1] %(inner%) or %(inner%|sep%) format specifiers. Here's an example:
> 
> import std;
> void main()
> {
>      {
>          alias NV = tuple;
>          auto arr = [NV("Steve", 1), NV("George", 500), NV("Adam", -5)];
>          writefln("%(%(%s: %s%), %)", arr);
>      }
> 
>      {
>          static struct NV
>          {
>              string name;
>              int value;
>          }
>          auto arr = [NV("Steve", 1), NV("George", 500), NV("Adam", -5)];
>          writefln("%(%(%s: %s%), %)", arr.map!(obj => obj.tupleof.tuple));
>      }
> }
> 
> In this case, from outside to inside, I am first formatting the range 
> and then for each tuple I am formatting its fields one by one.

Sweet! This is exactly what I was looking for.

> If for exmaple I want to format a tuple with 3 double, each one of them 
> with a different number of digits after the decimal point, I could do:
> "%(%.1f %.2f %.3f%)".writefln(tuple(1.5, 1.25, 1.125));

Nice. I think this should work well for me.

> I think we should extend std.format with support for using the same 
> tuple formatting specifier as std.typecons.Tuple, but for structs and 
> possibly classes, as I find it quite useful.

Yes. At least the mechanism you describe should be pasted into 
formattedWrite's spec as I had no idea about it, and I would not think 
to look at tuple docs for the answer.

A format spec that indicates formattedWrite should use tupleof and treat 
it the same would be nice instead of having to do map.tupleof.tuple.

-Steve