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digitalmars.D.bugs - [Issue 11235] New: Add analog of TypeTuple that does not auto-expand

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=11235

           Summary: Add analog of TypeTuple that does not auto-expand
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: public dicebot.lv



This topic pops up frequently in D.learn when one needs to pass several
distinct TypeTuple's as template arguments. Auto-expansion behavior of existing
TypeTuple does not make it possible because two will be merged into single
argument list.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=11235


Dicebot <public dicebot.lv> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull



https://github.com/D-Programming-Language/phobos/pull/1633

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrej.mitrovich gmail.com



14:34:46 PDT ---


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prev sibling next sibling parent d-bugmail puremagic.com writes:
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No, those are quite different. `std.typecons.Tuple` defines runtime tuple
(struct). It can be CTFE'ed of course, but it can't contain types (in TypeTuple
sense) or aliases (completely), only values and value meta-data.

Proposed `Group` acts exactly like `TypeTuple` but do not auto-expand.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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If TypleTuple comparison would have been legal, one could say that `Group!(int,
double, foo).expand == TypeTuple!(int, double, foo)`

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14:55:06 PDT ---


 No, those are quite different. `std.typecons.Tuple` defines runtime tuple
 (struct). It can be CTFE'ed of course, but it can't contain types (in TypeTuple
 sense) or aliases (completely), only values and value meta-data.
 
 Proposed `Group` acts exactly like `TypeTuple` but do not auto-expand.


Right.. well with Group you end up having a third tuple kind. I think it's best
that we wait for a language implementation of tuple syntax (see
http://wiki.dlang.org/DIP32).

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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It is not a 3d kind of tuple, it is just another syntax for existing TypeTuple.
Considering outcome of last tuple discussion threads any changes in that domain
won't come any time soon and this small addition allows to implement certain
algorithms right here and now.

I personally don't mind keeping it in "stdx" part of my projects but it is
mentioned quite frequently as a necessary feature [citation needed].

Also DIP32 addresses different issues and won't change the fact that both
expanding and non-expanding tuples are needed in different places.

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David Nadlinger <code klickverbot.at> changed:

           What    |Removed                     |Added
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                 CC|                            |code klickverbot.at



PDT ---
I wonder whether it is worth adding this as an officially supported kind of
tuple, or if we should encourage making creative use of the current syntax to
keep the complexity low: (untested, just typed it up to illustrate the
principle of nesting templates)

---
template isEqual(T...) {
  template to(U...) {
    static if (T.length == U.length) {
      static if (T.length == 0) {
        enum to = true;
      } else {
        enum to = isSame!(T[0], U[0]) && isEqual!(T[1 .. $]).to!(U[1 .. $])
      }
    } else {
      enum to = false;
    }
  }
}

static assert(isEqual!(1, 2, 3).to!(1, 2, 3));
---

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prev sibling parent d-bugmail puremagic.com writes:
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Main problem with nesting is that it does not allow algorithms with variadic
amount of tuples.

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