apply function to parameters

[Artur Skawina]

On 08/06/13 18:03, Dicebot wrote:
> On Tuesday, 6 August 2013 at 15:51:28 UTC, Jack Applegame wrote:
>> On Tuesday, 6 August 2013 at 14:44:18 UTC, bearophile wrote:
>>> Take a look at std.typetuple.staticMap
>> staticMap works with types, and I don't know how it can help.
> 
> Not really. Anything that can be provided to template argument list can be stored in TypeTuple and thus processed by staticMap. Name is very confusing here.

The problem is more that staticMap requires a *template*, not a
function. Another one is that doing it like that (ie storing the
intermediate results in a tuple or struct) creates unnecessary
copies -  which isn't really an issue for small PODs, because the
compiler optimizes most of the overhead away, but can have a
significant cost when handling types w/ nontrivial cpctors etc.

Anyway, there are several ways to do this in D. One example:

   void foo(Args...)(Args args) {
       mixin(evalExpMap!(q{ somefunc(%...); }, q{ process(%s) }, args));
         // == `somefunc(process(args[0]), process(args[1]), etc);`
   }

   // or

   void foo(Args...)(Args args) {
       auto result = mixin(evalExpMap!(q{ somefunc(%...) }, q{ process(%s) }, args));
       //...
   }

   // and the helper:

   template evalExpMap(string C, string F, A...) {
      enum evalExpMap = {
         import std.array, std.conv;
         string s, l;
         static if (is(typeof(A))) alias B = typeof(A);
                else               alias B = A;
         foreach (I, _; B) {
            auto r = replace( replace(F, "%s", A[I].stringof),
                                         "%d", to!string(I));
            l ~= (I?", ":"") ~ r;
            s ~=               r ~ ";\n";
         }
         return replace(replace(C, "%...;", s), "%...", l);
      }();
   }

Not as simple as the C++ equivalent. But not that much more
complicated and *much* more powerful.

artur