How to extend the string class to return this inside the square bracket?

[Marcone]

On Friday, 13 August 2021 at 23:08:07 UTC, jfondren wrote:
> On Friday, 13 August 2021 at 22:09:59 UTC, Marcone wrote:
>>
>> Isn't there some unario operator template that I can use with 
>> lambda to handle a string literal?
>
> So, something other than an exact "lit"[0..this.xx(..)] syntax 
> is fine?
>
> What didn't you like about `"Hello 
> World!".findSplit("o")[0].writeln;` then?
>
> What is a real example of something you want to do?

writeln("Hello World!"[x.indexOf("e")..x.indexOf("r")]);

indexOf()is just a simple example, not the goal. I want handle 
literal inside [] like it bellow, but in literal:

string x = "Hello World!";
writeln(x[x.indexOf("e")..x.indexOf("r")]);