Why does enumerate over range return dchar, when ranging without returns char?

[rikki cattermole]

On 03/05/2018 9:50 PM, ag0aep6g wrote:
> On 05/03/2018 07:56 AM, rikki cattermole wrote:
>>> ```
>>> import std.stdio;
>>> import std.range : enumerate;
>>>
>>> void main()
>>> {
>>>      char[] s = ['a','b','c'];
>>>
>>>      char[3] x;
>>>      auto i = 0;
>>>      foreach(c; s) {
>>>          x[i] = c;
>>>          i++;
>>>      }
>>>
>>>      writeln(x);
>>> }
>>> ```
>>> Above works without cast.
>>>
>>> '''
>>> import std.stdio;
>>> import std.range : enumerate;
>>>
>>> void main()
>>>      {
>>>      char[] s = ['a','b','c'];
>>>
>>>      char[3] x;
>>>      foreach(i, c; enumerate(s)) {
>>>          x[i] = c;
>>>          i++;
>>>      }
>>>
>>>      writeln(x);
>>> }
>>> ```
> [...]
>> The first example uses auto-decoding (UTF-8 codepoints into a single 
>> UTF-32 one). This is considered a bad thing. But the compiler can 
>> disable it and leave it as UTF-8 code point upon request.
> 
> The first example (foreach over a char[]) doesn't do any decoding. UTF-8 
> stays UTF-8.
> 
> Also, a `char` is a UTF-8 code *unit*, not a code *point*.
> 
>> The second example returns a Voldemort type (means no-name) which 
>> happens to be an input range. Where it can't disable anything and has 
>> been told that it is returning a dchar. See[0] as to where this gets 
>> decoded.
> 
> This is auto decoding.
> 
>> Writing two small functions to replace it (and popFront), will 
>> override this behavior.
> 
> This sounds like you can disable auto decoding by providing your own 
> range primitives in your own module. That doesn't work, because Phobos 
> would still use the ones from std.range.primitives.

Hmm, I swear this use to work.

Oh well, easy fix:

import std.algorithm;

struct Wrapper {
     char[] input;
     alias input this;

     @property char front() { return input[0]; }
     @property bool empty() {return input.length == 0;}
     void popFront() { input = input[1 .. $]; }
}

void main() {
  	char[] text = ['1', '2', '3'];

     foreach(c; Wrapper(text).filter!(a => a != '\0')) {
     	pragma(msg, typeof(c));
     }
}