Just another example of missing string interpolation

Fri Oct 20 07:14:45 UTC 2023

On 10/18/2023 7:47 PM, Adam D Ruppe wrote:
>> I'd like to see an example of code of how this customization might work, 
>> because I don't see it.
> 
> 
> Element makeHtmlFromTemplate(T...)(T t) if(T.length && is(T[0] == 
> core.interpolation.InterpolationHeader!Parts, Parts...)) {
>      string html;
>      foreach(idx, str; Parts) {
>        if(idx % 2 == 0)
>          html ~= str; // i know this is html string literal thanks to noramlization
>        else
>         // note i also know what code this came from in case i need it for error 
> messages, debug info, etc, it is in `str`
>          html ~= htmlEntitiesEncode(to!string(t[idx / 2]));
>      }
> 
>      return Element.make(Html(html));
> }
> 
> 
> auto element = makeHtmlFromTemplate(i`
>     <html>
>        <p class="foo" title="$(title)">
>             $(content)
>        </p>
>     </html>
> `);

Thanks for the example. I thought I'd show the equivalent with DIP1027. It's a 
bit crude, and I didn't bother with the details of html generation, but this 
shows the method and can be compiled and run:

```
import std.conv;

string makeHtmlFromTemplate(Parts...)(const char[] fmt, Parts parts)
{
     string html;
     size_t i;

     void advance()
     {
         while (i < fmt.length)
         {
             if (fmt[i] == '%' && i + 1 < fmt.length && fmt[i + 1] == 's')
             {
                 i += 2;
                 return;
             }
             html ~= fmt[i];
             ++i;
         }
     }

     advance();
     foreach (part; parts)
     {
         html ~= to!string(part); // or htmlEntityEncode
         advance();
     }
     return html;
}

void main()
{
     import std.stdio;
     string abc = "def";
     string html = makeHtmlFromTemplate("format %s %s sss", abc, 73);
          // tuple generated by DIP1027 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
          // from i"format $abc $(73) sss"
     writeln(html);
}
```
which prints:

format def 73 sss

This code can be adapted to do whatever output schema one wants. Compare the 
tuple generated by DIP1027:

```
tuple("format %s %s sss", abc, 73)
```
and with YAIDIP:
```
tuple(.object.imported!"core.interpolation".InterpolationHeader!("", "format ", 
"", abc, "", 73, "", " sss", ""), "", "format ", "", abc, "", 73, "", " sss", "")
```