The state of string interpolation

[Steven Schveighoffer]

On 12/6/18 5:03 PM, o wrote:
> I agree that lowering to a tuple opens up some cool possibilities, but 
> what about the times when it is desired to just use string interpolation 
> as just a plain string?
> For example, if `i"a is ${a}."` is equivalent to 'tuple("a is ", a, 
> ".")', then if you want to use the interpolated string as a string, you 
> would have to do something like `text(i"a is ${a}.")`. If this is the 
> case, how much better is this over a library implementation, which would 
> look like this: `interp!"a is ${a}."`?

`text(...)` is the way to go. Or rather `i"a is $a".text`;

And no, it wouldn't be interp!"a is $a.", as you HAVE to put mixin in 
there (this is how scriptlike works).

Consider if you are actually writing a string interpolation to do a 
mixin, it would be:

mixin(mixin(interp!"..."));

> 
> I am definitely not saying that a library solution is a better idea. I 
> personally think that this only makes sense as a language feature. But I 
> just think it would be best if `i"a is ${a}"` is more or less equivalent 
> to `"a is "~a.to!string~"."`.

I get what you are saying. But this solution is inferior for a few reasons:

1. It allocates. Maybe many times (lots of to!string calls allocate).
2. It loses information.
3. It depends on a library feature (i.e. unusable in betterC).

> As you said, string interpolation is just (very nice) syntactic sugar 
> over concatenation, so I think we should make this sugar as sweet as 
> possible.

It's sugar, but I'd prefer it to be D-flavored sugar. Expose what the 
developer wrote at compile-time, and let the language gurus work their 
magic. Concatenation is accessible, easily, but so are so many other 
things that make this very useful.

D is capable of doing so much, because of the ability to introspect, and 
discover at compile-time. I'm still freaking amazed that vibe.d can take 
a line like:

render!("myview.dt", foo, bar);

and process a DSL which has access to foo and bar, by those names, and 
outputs a compiled D function. I want to allow enabling such things with 
string interpolation too.

-Steve