Re: parameter pack to inputRange

[Ali Çehreli via Digitalmars-d-learn]

On 05/08/2016 04:48 PM, Erik Smith wrote:

On Sunday, 8 May 2016 at 22:37:44 UTC, Dicebot wrote:

On Sunday, 8 May 2016 at 14:11:31 UTC, Ali Çehreli wrote:

        E front() {
            final switch (index) {
                /* static */ foreach (i, arg; Args) {
                    case i:
                        return arg;
                }
            }
        }

AFAIK, this will do funny things with referencing stack if arguments
are variables and not literals.

Thanks! The static array version works for me too.   It would be good to
understand more about what is going on.  It looks like the cost of the
static array is an extra copy for each element. Maybe there is still a
way to avoid that.

I had to change one line of your test code. Dicebot's code work with it:

auto toInputRange (T...) (T args) @nogc
{
    import std.traits : CommonType;
    alias E = CommonType!T;

    struct Range
    {
        E[T.length] args;
        size_t index;

        E front () { return args[index]; }
        void popFront () { ++index; }
        bool empty () { return index >= args.length; }
    }

    Range range;
    foreach (i, ref arg; args)
        range.args[i] = arg;
    return range;
}

static void foo(Args...)(Args args) {
    import std.container.array;
    auto array = Array!int(toInputRange(args));  // <-- HERE

    foreach(a; array) {
        import std.stdio : writeln;
        writeln("e: ", a);
    }
}

void main ( )
{
    import std.stdio;
    writeln(toInputRange(1, 2, 3));

    foo(1,2,3);
}

It used to be

    toInputRange!(args)

Ali