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

[Marcone]

On Friday, 13 August 2021 at 23:21:42 UTC, Ali Çehreli wrote:
> On 8/13/21 4:08 PM, 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?
>
> And I started writing the following but stopped because the 
> semantics are not clear. I first called it 'between' but then 
> should the 'o' that was searched be a part of the output?
>
> Should "from 'o' to 'o'" produce an empty string, should it 
> include a single 'o' or should it go all the way to the next 
> 'o'?
>
> What about the last line which says "from 'd' to 'a'"? Is that 
> an entirely empty range or just 'd' or 'd' till the end?
>
> I don't think the programming language can decide one way or 
> the other.
>
> import std.algorithm;
> import std.range;
> import std.stdio;
>
> auto inclusive(R, E)(R range, E fromNeedle, E toNeedle) {
>   auto found = range.find(fromNeedle);
>   return chain(found.front.only, 
> found.drop(1).findSplitAfter(only(toNeedle))[0]);
> }
>
> void main() {
>   const s = "Hello World!";
>   auto r = s.inclusive('o', 'o');
>   writeln(r);
>
>   writeln("abcdef".inclusive('d', 'a'));
> }
>
> Ali


import std;

class None {}
// Function slice()
auto slice(T1, T2, T3 = None)(T1 conteudo, T2 inicio, T3 fim = 
T3.init) {
	int start, end, startlen;
	static if (is(T2 == int)) {inicio = inicio < 0 ? conteudo.length 
+ inicio : inicio;}
	static if (is(T3 == int)) {fim = fim <= 0 ? conteudo.length + 
fim : fim;}
	static if (is(T2 == int)) {start = inicio;} else static if 
(is(T2 == string)){start = conteudo.countUntil(inicio);}
	static if (is(T2 == string)) {static if (is(T1 == 
string)){startlen = start + inicio.length + 1;} else {startlen = 
start + 1;}}
	static if (is(T3 == int)) {end = fim;} else static if (is(T3 == 
string)){end = startlen + conteudo[startlen..$].countUntil(fim);}
	static if (is(T3 == None)) {return conteudo[start];} else 
{return conteudo[start..end];}
}

void main(){
	writeln("Hello World!".slice(1, 8)); // ello Wo
	writeln("Hello World!".slice("e", "r")); // ello Wo
	writeln("Hello World!".slice(1, "r")); // ello Wo
	writeln("Hello World!".slice("e", 8)); // ello Wo
	writeln("Hello World!".slice(6, -1)); // World (Same as $-1)
	writeln("Hello World!".slice(-12, -7)); // Hello (Same as $-12, 
$-7)
	writeln("Hello World!".slice("W", -1)); // World (Same as "W", 
$-1)
	writeln("Hello World!".slice(-12, " ")); // Hello (Same as $-12, 
" ")
}

Like this function, but inside []. So I can use functions to get 
index for slice.