Now that's a DIP that could use some love

[Andrei Alexandrescu]

On 9/18/20 4:13 AM, Timon Gehr wrote:
> On 17.09.20 23:55, Andrei Alexandrescu wrote:
>>
>> Flag!"each" each(Range) (
>>    Range r
>> )
>> if (!isForeachIterable!Range && (isRangeIterable!Range || 
>> __traits(compiles, typeof(r.front).length)));
> 
> So `each` says it works for types that cannot be iterated with `foreach` 
> but whose `front` has a `length` member? :-)
> 
> Turns out it does not:
> 
> ----
> import std.algorithm;
> struct S{
>      struct T{
>          struct Q{}
>          Q length;
>      }
>      T front;
> }
> 
> void main(){
>      S().each!((x){});
> }
> ----
> std/algorithm/iteration.d(966): Error: template 
> `std.range.primitives.empty` cannot deduce function from argument types 
> `!()(S)`, candidates are:
> ...
> ----
> 
> https://issues.dlang.org/show_bug.cgi?id=21264

Thanks. It's interesting that those who opined the constraints are 
pretty easy to read didn't even notice this one's wrong. If you think 
it's easy and got it wrong, it's not easy!

Second, the same argument applies to assert. Why provide a string with 
the assert when all it does is it repeats the expression in human 
language? Yet most asserts do provide explanatory strings, and I can 
only assume many people find those useful.

The mechanics is not the design.