More fun with autodecoding

[Steven Schveighoffer]

On 9/13/18 3:53 PM, H. S. Teoh wrote:
> On Thu, Sep 13, 2018 at 06:32:54PM -0400, Nick Sabalausky (Abscissa) via Digitalmars-d wrote:
>> On 09/11/2018 09:06 AM, Steven Schveighoffer wrote:
>>>
>>> Then I found the true culprit was isForwardRange!R. This led me to
>>> requestion my sanity, and finally realized I forgot the empty
>>> function.
>>
>> This is one reason template-based interfaces like ranges should be
>> required to declare themselves as deliberately implementing said
>> interface. Sure, we can tell people they should always `static
>> assert(isForwardRage!MyType)`, but that's coding by convention and
>> clearly isn't always going to happen.

No, please don't. I've used C# and Swift, and this sucks compared to 
duck typing.

> Yeah, I find myself writing `static assert(isInputRange!MyType)` all the
> time these days, because you just never can be too sure you didn't screw
> up and cause things to mysteriously fail, even though they shouldn't.
> 
> Although I used to be a supporter of free-form sig constraints (and
> still am to some extent) and a hater of Concepts like in C++, more and
> more I'm beginning to realize the wisdom of Concepts rather than
> free-for-all ducktyping.  It's one of those things that work well in
> small programs and fast, one-shot projects, but don't generalize so well
> as you scale up to larger and larger projects.

The problem I had was that it wasn't clear to me which constraint was 
failing. My bias brought me to "it must be autodecoding again!". But 
objectively, I should have examined all the constraints to see what was 
wrong. All C++ concepts seem to do (haven't used them) is help identify 
easier which requirements are failing.

We can fix all these problems by simply identifying the constraint 
clauses that fail. By color coding the error message identifying which 
ones are true and which are false, we can pinpoint the error without 
changing the language.

Once you fix the issue, it doesn't error any more, so the idea of duck 
typing and constraints is sound, it's just difficult to diagnose.

-Steve