DIP 1027--String Interpolation--Final Review Discussion Thread

[Steven Schveighoffer]

On 2/2/20 9:29 AM, Adam D. Ruppe wrote:
> On Sunday, 2 February 2020 at 14:20:16 UTC, Timon Gehr wrote:
>> This is a use case for `alias this`, the language just has to support it.
> 
> Indeed.
> 
> So is
> 
> string s = i"";
> 
> so idk which one we'd use (unless the language gets multiple alias this 
> lol).
> 
> But regardless the struct lets us have it all. With alias this it is 
> every minor detail. Without it it is a simple method call.
> 
> I used to lukewarm support this DIP, but since the struct is so much 
> better, superior in almost every objective measure, I now think we 
> should vote it down unless it changes.

The problem I have with the struct mechanism is that it enforces the 
parameters are all non-reffable data.

e.g., this should work with the DIP as proposed:

int apples;
int bananas;
readf(i"I have $apples apples and $bananas bananas");

I don't know how you do that with a struct as the result of the 
interpolated string without knowing how the parameters will be used.

Or this:

struct S {}
foo!(i"I'm passing $S as an alias/type, with some formatting data around 
it");

Other than that, I like the idea of the struct for the purposes of 
overloading. I still would like the format string to be a custom type 
that devolves to string. I also liked the straight conversion to a tuple 
where every other parameter was a string (i.e. Marler's implementation).

The biggest thing that the DIP has going for it is that there are lots 
of functions which have a format string + args, due to the way D/C does 
varargs, and this will be a drop-in call without having to change any 
code or add special overloads. The whole printf thing is meh to me, I 
don't use it and don't care to use it with this mechanism anyway (writef 
is a different story).

And Walter:
C functions aren't overloadable?

This works just fine:

---------
import core.stdc.stdio : printf;

void printf(int x) { printf("%d", x); }

void main()
{
     printf("hello %d\n", 5);
     printf(5);
     printf("\n");
}

---------

output:

hello 5
5

-Steve