Re: Unpacking Slices

[Ali Çehreli via Digitalmars-d-learn]

On 6/14/21 11:08 AM, Justin Choi wrote:
Is there any shortcut for unpacking slices like I'd want to do in a 
scenario like this?
`info = readln.strip.split;`
`string a = info[0], b = info[1], c = info[2];`

D does not have automatic unpacking. Here is a quick, dirty, and fun 
experiment:

struct Unpack(Args...) {
  static string typeName(size_t n)() {
    return Args[n].stringof;
  }

  static char varName(size_t n) {
    return cast(char)('a' + n);
  }

  // Variable declarations
  static foreach (n; 0 .. Args.length) {
    mixin (typeName!n ~ ' ' ~ varName(n) ~ ';');
  }

  // Get by variable number
  auto get(size_t n)() {
    mixin ("return " ~ varName(n) ~ ';');
  }

  // Set by variable number
  auto set(size_t n, T)(T value) {
    mixin (varName(n) ~ " = value;");
  }
}

template unpack(Args...) {
  auto unpack(R)(R range) {
    auto result = Unpack!(Args)();
    static foreach (n; 0 .. Args.length) {
      import std.range : front, popFront;
      result.set!n(range.front);
      range.popFront();
    }
    return result;
  }
}

import std.stdio;
import std.string;

void main() {
  auto info = readln.strip.split;
  auto u = info.unpack!(string, string, string);

  // Variables are accessed by name as a, b, etc. or by number:
  assert(u.a == u.get!0);
  assert(u.b == u.get!1);
  assert(u.c == u.get!2);
}


When all variable types are the same, the usage can be improved to allow 
e.g.

  info.unpack!(3, string)

That's not implemented yet. :)

Ali