writing iterators without code duplication. inout?

[Andrew Wiley]

On Thu, Dec 22, 2011 at 12:04 AM, pompei2 <pompei2 at gmail.com> wrote:
>> int delegate(int delegate(ref int)) doIter() const
>>  {
>> 74      return (int delegate(ref int) dg)
>>      {
>>        cast(typeof(this))(this).doIter()
>> 77            (
>> 78              (ref int i)
>>
>>              {
>>                int copy = i; dg(copy);
>>              }
>>          );
>>      }
>>  }
>
>
> I see what you are doing there. Unfortunately, the innermost delegate (the
> one doing the copy trick) somehow got @system attribute, which leads to the
> following compile errors (I added line numbers and reordered your code in
> the citation above):
>
> constiter.d(78): Error: cannot implicitly convert expression (__dgliteral2)
> of type void delegate(ref int i) @system to int delegate(ref int)
> constiter.d(77): Error: cast has no effect in expression
> (cast(const(Container))this.doIter()((__error)))
> constiter.d(74): Error: cannot implicitly convert expression (__dgliteral1)
> of type void delegate(int delegate(ref int) dg) @system to int delegate(int
> delegate(ref int))
>
> Where does this @system come from? How do I get rid of it?

Actually, it looks like your issue is here:
constiter.d(78): Error: cannot implicitly convert expression
(__dgliteral2) of type *void* delegate(ref int i) @system to int
delegate(ref int)

void delegate(ref int) != int delegate(ref int)