[Issue 9009] allow foreach without identifier

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=9009

--- Comment #7 from bearophile_h...@eml.cc ---
With a little breaking change "_" could become a name that can't be referenced,
so you can do:

foreach (_; 0 .. 10) { // OK
  foreach (_; 0 .. 20) { // OK
    writeln(_); // syntax error
  }
}


Such _ can also be used as "don't care" for tuple unpacking:

t{_, b} = fooAB();


And in switch on structs (that contain the optional "unapply" method):

switch (foo) {
  case Foo(x, _, _): writeln(x); break;
  default:
}

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