What do you thing about this string interpolation idea

[Jonathan Marler]

On Monday, 10 December 2018 at 16:45:30 UTC, Steven Schveighoffer 
wrote:
> On 12/10/18 11:36 AM, Aliak wrote:
>> On Monday, 10 December 2018 at 16:27:03 UTC, Steven 
>> Schveighoffer wrote:
>>> On 12/10/18 11:11 AM, aliak wrote:
>>>> This is much better than having to mixin everywhere. A 
>>>> couple of things:
>>>>
>>>> 1) Can this be put in a module so that you don't have to 
>>>> mixin(enableInterpolation) but instead "import interp = 
>>>> std.interpolation;" or something similar?
>>>
>>> No, you need a local mixin. Doing that import just imports 
>>> the *symbol* into your namespace, but it doesn't give access 
>>> to your namespace to the symbol.
>>>
>> 
>> Au :(. Yeah that makes sense. Then I’m not sure I see how this 
>> improves things if it has to be mixed in to every scope you 
>> want to use interpolation for. The sparseness of interpolation 
>> might just make mixin(Interp!””)); more appealing.
>
> The benefit is that you only have to mixin once, whereas the 
> usage does not require a mixin. It just goes next to your 
> import statements.
>
> However, multiple scopes may make this less appealing, as you 
> would have to mixin at any inner scope that has a variable you 
> want to deal with.
>
> But I plan to write some string interpolation libraries based 
> on this, would love to see a "better SQL" library for something 
> like this.
>
> Not sure if it mitigates the need for an interpolation DIP, as 
> clearly this is going to be compile-time intensive, where the 
> cleverness is stomped on by memory usage and slow compile times.
>
> -Steve

It can also have some pretty unexpected results.  For example, 
having a variable reference an outerscope instance instead of the 
local one:

import std.stdio;
template somefun()
{
      auto iterpolate(string s)()
      {
          //do some parsing
          return mixin(s[1 .. $]);
      }
}

enum enableInterpolate = "mixin somefun A; alias interpolate = 
A.iterpolate;";

mixin(enableInterpolate);
enum a = 10;
enum msg = iterpolate!("$a");

void main()
{
     int a = 5;
     iterpolate!("$a").writeln;
}

This prints 10.