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

[ag0aep6g]

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.

> [0] https://dlang.org/phobos/std_range_primitives.html#.front