making a struct an inputRange with free functions

[Johannes Loher]

Am 16.04.2018 um 21:27 schrieb Jonathan M Davis:
> On Monday, April 16, 2018 21:10:03 Johannes Loher via Digitalmars-d-learn 
> wrote:
>> Is there a way to do this? Here is a naive implementation:
>> https://run.dlang.io/is/JKvL80 .
>>
>> It does not pass `isInputRange` (I think, because the free functions are
>> not visible in the scope of `isInputRange`).
>>
>> Trying to iterate over it with a foreach loop results in a compile error:
>> Error: invalid foreach aggregate NoRange(0, 0).this(5), define
>> opApply(), range primitives, or use .tupleof
>>
>> Thanks for your help!
> 
> It doesn't work unless the module using the range either contains the free
> functions or imports them. So, I believe that that would mean that for
> isInputRange to pass, std.range.primitives would have to have access to the
> functions, which isn't going to happen for anything but dynamic arrays. It's
> a limitation of UFCS in general (it's similar to why using string lambdas
> with std.functional has become fairly rare - you can only use functions in
> them that std.functional already knows about). The only way for the
> functions to be associated with the type and thus always be available is if
> they're member functions. So, if you want a type to be a range, you have to
> declare the range functions as member functions.
> 
> - Jonathan M Davis
> 
Yeah, that's what I guessed, too. Thanks for the clarification.