DIP 1027---String Interpolation---Community Review Round 1

[Patrick Schluter]

On Monday, 16 December 2019 at 12:37:47 UTC, Jacob Carlborg wrote:
> On Monday, 16 December 2019 at 11:18:33 UTC, Patrick Schluter 
> wrote:
>
>> Maybe I'm wrong here, I haven't thought it through, but in 
>> first approach I think that's an essential point. As the 
>> string contains code, if evaluated at CT, the string must be 
>> split somehow in literal parts and code parts. Allowing the 
>> i-string to be handled as regular string implies that the 
>> splitting happens sometime between when it is declared and 
>> after it is used, which can happen after runtime.
>>
>> import fn;
>>
>> int b = 20;
>>
>> string inter = i"$(a+b)";
>>
>> foreach(a; 1..10)
>>   fn(inter);
>>
>> ---
>> module fn;
>>
>> void fn(string s)
>> {
>>   writefln(s);
>> }
>>
>> How would that work?
>>
>> In python or javascript there's no issue, a is a runtime 
>> symbol.
>
> Not sure how other languages do it but in Ruby the 
> interpolation is performed where the string literal is 
> declared. Not where the string is later used. So the above 
> would fail because  `a` is not available.
>
Yes, probably. The issue I had with the transformation as string 
is what should the code below print?

import fn;

int a, b = 20;

string inter = i"$(a+b)";

for(a=0; a<10; a++)
    fn(inter);

  ---
  module fn;

  void fn(string s)
  {
    writef(s);
  }

prints
202020202020202020

or

212223242526272829

and that's the difference between CT evaluation and RT evaluation.