The Case For Autodecode

[Steven Schveighoffer via Digitalmars-d]

On 6/3/16 1:51 PM, Patrick Schluter wrote:
> On Friday, 3 June 2016 at 11:24:40 UTC, ag0aep6g wrote:
>> This is mostly me trying to make sense of the discussion.
>>
>> So everyone hates autodecoding. But Andrei seems to hate it a good bit
>> less than everyone else. As far as I could follow, he has one reason
>> for that, which might not be clear to everyone:
>>
>> char converts implicitly to dchar, so the compiler lets you search for
>> a dchar in a range of chars. But that gives nonsensical results. For
>> example, you won't find 'ö' in  "ö".byChar, but you will find '¶' in
>> there ('¶' is U+00B6, 'ö' is U+00F6, and 'ö' is encoded as 0xC3 0xB6
>> in UTF-8).
>
> You mean that '¶' is represented internally as 1 byte 0xB6 and that it
> can be handled as such without error? This would mean that char literals
> are broken. The only valid way to represent '¶' in memory is 0xC3 0x86.
> Sorry if I misunderstood, I'm only starting to learn D.

Not if '¶' is a dchar.

What is happening in the example is that find is looking at the 
"ö".byChar range and saying "hm... can I compare dchar('¶') to char? 
Well, char implicitly casts to dchar, so I'm good!", but a direct cast 
of the bits from char does NOT mean the same thing as a dchar. It has to 
go through a decoding first.

The real problem here is that char implicitly casts to dchar. That 
should not be allowed.

-Steve