How do I index a function parameter tuple with a run-time index?

On 15.01.2016 21:42, Nordlöw wrote:
> How do I index a function parameter tuple with a run-time index?

With a switch and a static foreach:

----
void f(A...)(size_t i, A a)
{
    import std.stdio: writeln;
    switch_: switch (i)
    {
        foreach (iT, T; A)
        {
            case iT: writeln(T.stringof); break switch_;
        }
        default: writeln("??"); break;
    }
}

void main()
{
    f(0, "foo", 42); /* string */
    f(1, "foo", 42); /* int */
    f(2, "foo", 42); /* ?? */
}
----

On Friday, 15 January 2016 at 20:42:47 UTC, Nordlöw wrote:
> How do I index a function parameter tuple with a run-time index?

I believe it's impossible because a parameter tuple is not a runtime entity. If it was an expression tuple (a compile-time tuple of only values, no types or symbols) and all of the values had a common base type, you could put it in an array and index that.

On Friday, 15 January 2016 at 20:48:39 UTC, anonymous wrote:
> On 15.01.2016 21:42, Nordlöw wrote:
>> How do I index a function parameter tuple with a run-time index?
>
> With a switch and a static foreach:
>
> ----
> void f(A...)(size_t i, A a)
> {
>     import std.stdio: writeln;
>     switch_: switch (i)
>     {
>         foreach (iT, T; A)
>         {
>             case iT: writeln(T.stringof); break switch_;
>         }
>         default: writeln("??"); break;
>     }
> }
>
> void main()
> {
>     f(0, "foo", 42); /* string */
>     f(1, "foo", 42); /* int */
>     f(2, "foo", 42); /* ?? */
> }
> ----

And of course I'm proven wrong as soon as I post :) Sometimes I forget how powerful D's  code generation abilities are.

On Fri, 15 Jan 2016 20:52:46 +0000, Meta wrote:

> And of course I'm proven wrong as soon as I post :) Sometimes I forget how powerful D's  code generation abilities are.

Username doesn't check out, :(

On Friday, 15 January 2016 at 21:47:21 UTC, Justin Whear wrote:
> On Fri, 15 Jan 2016 20:52:46 +0000, Meta wrote:
>
>> And of course I'm proven wrong as soon as I post :) Sometimes I forget how powerful D's  code generation abilities are.
>
> Username doesn't check out, :(

Huh?