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

[Marcone]

On Friday, 13 August 2021 at 21:14:29 UTC, user1234 wrote:
> On Friday, 13 August 2021 at 21:05:22 UTC, Marcone wrote:
>> How to extend the string class to return this inside the 
>> square bracket the same way opDollar $ returns the length of 
>> the string? Thank you.
>>
>>     import std;
>>
>>     void main(){
>>     	writeln("Hello World!"[0..this.indexOf("o")]);
>>     }
>
> this does not exist (and see few reason for) but algo + ufcs 
> allows this easily, e.g
>
> ```
> "Hello World!".findSplit("o")[0].writeln;
> ```
>
> bonus: both can throw bound error

My example was just an example. I don't want this solution. I 
want to have the power to handle the string inside the square 
brackets.