import std.typecons;

import std.stdio;

​

void main() {

    writeln("OK:");

    ok();

    writeln("\nNOT OK:");

    notOk();

}

​

void ok() {

    auto r = refCounted(Range());

    writeln("before ", r.front);

    for (auto __rangeCopy = r; !__rangeCopy.empty; __rangeCopy.popFront())

        writeln("loop ", __rangeCopy.front);

​

    writeln("after ", r.front);

    assert(r.i == 3, "r.i != 3");

}

​

void notOk() {

    auto r = refCounted(Range());

    writeln("before ", r.front);

    foreach (i; r)

        writeln("loop ", i);

    writeln("after ", r.front);

    assert(r.i == 3, "r.ri != 3");

}

​

struct Range {

    int i;

    // @disable this(this); // uncomment this line and notOk() fails to compile at foreach

​

    bool empty() {

        return i == 3;

    }

​

    void popFront() {

        i++;

    }

​

    int front() {

        write("addr ", &this, ": ");

        return i;

    }

}

​