Input/Output multiple values from function

[Ali Çehreli]

On 08/27/2019 10:17 PM, Jabari Zakiya wrote:

 > I can't do (a, b, c,d) = func1(i) directly.
 > What do I do to assign the output of func1 to the individual variables?

I had some time to play with the following syntax, similar usage of 
which has been proposed a number of times as a replacement for tuple 
expansion. Assuming that foo() returns a struct of int, double, string; 
the following expression will set the variables to those members:

   int i;
   double d;
   string s;

   foo(42).into!(i, d, s);

Here is the complete program:

import std.stdio;
import std.string;

struct S {
   int i;
   double d;
   string s;
}

S foo(int i) {
   return S(i, 1.5, "hi");
}

template into(args...) {
   auto into(From)(From from)
   if (is (From == struct))
   {
     static foreach (i, m; __traits(allMembers, From)) {{
       alias argT = typeof(args[i]);
       alias memT = typeof(__traits(getMember, from, m));
       static assert (is (argT == memT),
                      format!"Cannot expand '%s %s.%s' into '%s %s' 
argument."
                      (memT.stringof, From.stringof, m, argT.stringof, 
args[i].stringof));
       mixin (format!"args[%s] = from.%s;"(i, m));
     }}
   }
}

void main() {
   int i;
   double d;
   string s;

   foo(42).into!(i, d, s);

   writeln(i);
   writeln(d);
   writeln(s);
}

I know that it does not address attributes like shared, etc. but it 
shows how expressive nested templates can be.

Ali