opSlice and foreach with ranges

[Ali Çehreli]

Is that not implemented yet?

TDPL mentions a very useful feature on page 381 under "12.9.1 foreach 
with Iteration Primitives".

(Note: I am copying all of this manually; the typos are mine):

It first shows a function that includes a possible "compiler rewrite" of 
a foreach loop:

void process(SimpleList!int lst) {
    for (auto __c = lst; !__c.empty; __c.popFront()) {
        auto value = __c.front;
        ... // Use value of type int
    }
}

It then says

<quote>
... if the iterated object offers the slice operator with no arguments 
lst[], __c is initialized with lst[] instead of lst. This is in order to 
allow "extracting" the iteration means out of a container without 
requiring the container to define the three iteration primitives.
</quote>

I couldn't get that to work with the following code:

import std.stdio;

struct MyRange
{
    int theOnlyOne;

    @property bool empty() const
    {
        return false;
    }

    @property ref int front()
    {
        return theOnlyOne;
    }

    void popFront()
    {}
}

struct MyCollection
{
    MyRange opSlice() const
    {
        return MyRange();
    }
}

void main()
{
    auto coll = MyCollection();

    foreach (i; coll) {            // <-- compilation error
        // ...
    }
}

Error: cannot infer type for i

Providing the type of i as 'int' or 'ref int' produce a different error:

    foreach (int i; coll) {

or

    foreach (ref int i; coll) {

produce

Error: no property 'opApply' for type 'MyCollection'

Please note that taking a slice explicitly works:

    foreach (i; coll[]) {

but not the feature mentioned in TDPL.

Thank you,
Ali