Invalid foreach aggregate

[Chris via Digitalmars-d-learn]

On Tuesday, 17 November 2015 at 11:26:19 UTC, Marc Schütz wrote:

>
> That really depends on the details, that's why I asked. It 
> could be a regression, or it could be that the compiler now 
> does stricter checking than before, and your implementation 
> wasn't completely correct, or it could be a bug in Phobos if 
> you use that to create the range.
>
> If you can post a minimal example that works in 2.067.1, but 
> doesn't with the current version, I can try to find the change 
> that broke it.

I did just that and I could find the culprit. It's opIndex(). It 
works up until 2.068.0, with 2.068.1 I already get this error:

"primitives.d(7): Error: invalid foreach aggregate 
doSomething(items).opIndex()"

Here's the example:

=========================

import std.stdio : writeln;
import std.range.primitives;

void main()
{
   string[] items = ["a", "b", "c"];
   foreach (ref it; items.doSomething())
   {
     writeln(it);
   }
}

auto doSomething(InputRange)(ref InputRange r)
{
   struct DoSomething
   {
     private
     {
       InputRange r;
       size_t cnt;
     }

     this(InputRange r)
     {
       this.r = r;
     }

     @property bool empty()
     {
       return r.length == 0;
     }

     @property auto front()
     {
       return r[0];
     }

     @property void popFront()
     {
       r = r[1..$];
     }

     @property size_t length() const
     {
       return r.length;
     }

     @property size_t opIndex()
     {
       return cnt;
     }

     @property auto save() const
     {
	return this;
     }
   }

   return DoSomething(r);
}