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digitalmars.D.bugs - [Issue 5037] New: std.variant.Algebraic test use case

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5037

           Summary: std.variant.Algebraic test use case
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: bearophile_hugs eml.cc


--- Comment #0 from bearophile_hugs eml.cc 2010-10-10 14:42:54 PDT ---
Created an attachment (id=781)
One memory/runtiume performance test for the compiler/binary for the flatten

This isn't a bug report.

In dmd 2.049 the docs for std.variant.Algebraic state:

 BUGS: Currently, Algebraic does not allow recursive data types.
 They will be allowed in a future iteration of the implementation. 
Once that limit is lifted, the following problem may be used to see if the API of Algebraic is well designed. The problem is, given an arbitrary nested list of values and sublists: [[1], 2, [[3,4], 5], [[[]]], [[[6]]], 7, 8, []] To flatten it fully into this result: [1, 2, 3, 4, 5, 6, 7, 8] This is a solution that minimizes heap activity, it doesn't use Algebraic but it uses a tagged union: import std.stdio: writeln; import std.conv: to; struct TreeList(T) { union { TreeList!T[] arr; T data; } bool isArray = true; static TreeList!T opCall(Types...)(Types items) { TreeList!T result; foreach (i, el; items) static if (is(Types[i] == T)) { TreeList!T item; item.isArray = false; item.data = el; result.arr ~= item; } else result.arr ~= el; return result; } TreeList!T flatten() { TreeList!T result; if (this.isArray) foreach (el; this.arr) result.arr ~= el.flatten().arr; else result.arr ~= this; return result; } string toString() { if (isArray) return to!string(arr, "[", ", ", "]"); else return to!string(data); } } void main() { alias TreeList!(int) L; // 12 bytes if T is int auto l = L(L(1), 2, L(L(3,4), 5), L(L(L())), L(L(L(6))), 7, 8, L()); writeln(l); writeln(l.flatten()); } Well implemented Algebraic types are supposed to allow a shorter, simpler and equally runtime/memory-efficient solution to this problem (the efficiency may be tested with the large list literal in the attach file). -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 10 2010
parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5037


Andrei Alexandrescu <andrei metalanguage.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |andrei metalanguage.com
         AssignedTo|nobody puremagic.com        |andrei metalanguage.com


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