On 08/10/2016 11:08 AM, Lodovico Giaretta wrote:
> I'm probably missing something stupid but...
> Why on earth do the two loops in main print a different result?
> It looks like the foreach lowering is ignoring my definition of front...
>
> =====================================================
> import std.stdio, std.container.array;
>
> struct RangeWrapper(Range)
> {
> Range range;
> alias range this;
>
> auto front()
> {
> return range.front + 1;
> }
> }
> auto rangeWrapper(Range)(auto ref Range range)
> {
> return RangeWrapper!Range(range);
> }
>
> void main()
> {
> Array!int array;
> array.insertBack(3);
>
> foreach (i; rangeWrapper(array[]))
> writeln(i); // prints 3, which is wrong
>
> // isn't the above foreach equivalent to the following loop ?
>
> for (auto r = rangeWrapper(array[]); !r.empty; r.popFront())
> writeln(r.front); // correctly prints 4
> }
> =====================================================
>
> Thank you for your help.
RangeWrapper does not provide the InputRange interface, so the compiler
uses 'alias this' and iterates directly on the member range.
I tried making RangeWrapper an InputRange but failed. It still uses 'range'.
// Still fails with these:
@property bool empty() {
return range.empty;
}
void popFront() {
range.popFront();
}
I don't know how the decision process works there.
Ali
