import std.traits;

struct Lock
{
    static opCall ()
    {
        Lock l;
        l.lock();

        return l;
    }

    ~this ()
    {
        unlock();
    }

private:

    void lock () {}
    void unlock () {}
}


void lock (T) (T value, void delegate (Unqual!(T)) dg)
{
    auto l = Lock();
    dg(castAwayShared(value));
}

void main ()
{
    shared int i;
    lock(i, (x) {
        // operate on i
    });
}