New Lookup Table (MixString)

[Salih Dincer]

Hi,

This is an InputRange and RandomAccessRange combined; it's also 
the placement of wchar in possible null parts of dchar.

Please criticize this code. Each element of a UTF string is 
matched to its counterparts as dchar and used as wchar. The code 
is self-explanatory, do you think it's useful?

```d
import std.stdio, std.algorithm;
import std.range, std.conv;

enum alphabets
{
   u = "ÂABCÇDEFGHIJKLMNOPQRSTUVĞİWXYZÖŞÜÇÎÛ",
   l = "âabcçdefghıjklmnopqrstuvğiwxyzöşüçîû",

   ASCII65_95 = "AABCCDEFGHIJKLMNOPQRSTUVGIWXYZOSUCIU",
   ASCII96_127 = "aabccdefghijklmnopqrstuvgiwxyzosuciu",
   ASCII65_127 = ASCII65_95 ~ ASCII96_127
}

//enum dictU = alphabets.u.to!(wchar[]);
enum dictU = "ÂABCÇDEFGHIJKLMNOPQRSTUVĞİWXYZÖŞÜÇÎÛ".to!(wchar[]);
enum dictL = alphabets.l.to!(wchar[]);

struct MixString(T, T[] leftLiterals)
{
   size_t index;
   dchar[] dict;

   this(string d)
   {
     // load dictionary
     foreach(dchar c; d) dict ~= c;

     // place counterparts
     foreach(i, wchar c; leftLiterals)
     {
       dict[i] |= c << 16;
     }
   }

   // input range functions
   bool empty() { return index == dict.length; }
   T front() { return dict[index] & 0x0000_FFFF; }
   void popFront() { ++index; }

   // search elements
   auto nextIndexOf(wchar key)
   {
     scope(exit) index = 0;

     size_t i = 1;
     while(!empty)
     {
       if(front == key)
       {
         return i;
       } else i++;
       popFront();
     }
     return 0;
   }
}
//
alias ConvUpper = MixString!(wchar, dictU);
alias ConvLower = MixString!(wchar, dictL);

void main()
{
   auto test = ConvUpper(alphabets.l);/*
   foreach(wchar c; test)
   {
     c.writefln!"%4X: %s"(c);
   }//*/

   string text = "fıstıkçı şâhap bir insandır!";
   foreach(wchar c; text)
   {
     if(auto result = test.nextIndexOf(c))
     {
       wchar lookup = test.dict[result - 1] >> 16;
       lookup.write;
     } else
       c.write;
   }
   writeln;
}
/*

FISTIKÇI ŞÂHAP BİR İNSANDIR!

*/
```

SDB at 79